Ruth B. Lathi
Danny J. Schust
• Isolated spontaneous pregnancy loss is remarkably common. Recurrent pregnancy loss affects between 1 in 300 and 1 in 100 couples.
• After several pregnancy losses, there remains a greater chance of having a viable birth than another loss, even without treatment. Prognosis can improve dramatically with treatment of a known underlying etiology for recurrent pregnancy loss.
• Parental chromosomal abnormalities and the antiphospholipid syndrome (APS) are the only undisputed causes of recurrent pregnancy loss. Other well-described causes include anatomic, endocrine, thrombotic, and possibly other immunologic factors.
• The state of coagulability is a fine balance between pro- and antithrombotic pathways. The hypercoagulability of pregnancy can be attributed to increases in prothrombotic factors and decreases in those that inhibit coagulation.
• The immunologic interactions at the maternal–fetal interface reflect the presence of unique cellular constituents combined with the actions of steroid hormones, protein hormones, and metabolic factors.
• Evaluation of patients with recurrent pregnancy loss should include a detailed patient and family history, an examination focused on endocrine and anatomic abnormalities, and laboratory studies limited to evaluation of treatable etiologies.
• Monitoring early pregnancies in recurrent pregnancy loss patients should include ultrasound, β-human chorionic gonadotropin levels if indicated, frequent visits with psychological support, and the karyotypic analysis of tissues from any pregnancy losses.
• In treating recurrent pregnancy loss, evidence supports repairing anatomic abnormalities, correcting preexisting endocrine disorders, and treating APS and other thrombophilic disorders.
Advances in the ability to document and diagnose early pregnancy reveal that spontaneous pregnancy loss is a common event. Spontaneous pregnancy loss is, in fact, the most common complication of pregnancy. Approximately 70% of human conceptions fail to achieve viability, and an estimated 50% are lost before the first missed menstrual period (1). Most of these pregnancy losses are unrecognized. Studies using sensitive assays for human chorionic gonadotropin (hCG) indicate that the actual rate of pregnancy loss after implantation is 31% (2). Loss occurs in 15% of pregnancies that are clinically recognized before 20 weeks of gestation from last menstrual period (3,4).
Traditionally, recurrent abortion has been defined as the occurrence of three or more clinically recognized pregnancy losses before 20 weeks from the last menstrual period. Using this definition, recurrent pregnancy loss occurs in approximately 1 in 300 pregnancies (2). Clinical investigation of pregnancy loss, however, may be initiated after two consecutive spontaneous abortions, especially when fetal heart activity is identified before any of the pregnancy losses, when the women is older than 35 years of age, or when the couple has had difficulty conceiving (5). A study of over 1,000 patients with recurrent pregnancy loss reported no difference in the prevalence of abnormal results for evidence-based and investigative diagnostic tests when the diagnostic workup was initiated after two versus three or more losses (6). If clinical intervention is undertaken in the form of investigation after two spontaneous abortions, approximately 1% of pregnant women will require evaluation (3). Even with a history of recurrent pregnancy loss, a patient is more likely to carry her next pregnancy successfully to term than to miscarry. For patients with a history of recurrent pregnancy loss, the risk of subsequent pregnancy loss is estimated to be 24% after two clinically recognized losses, 30% after three losses, and 40% to 50% after four losses (7). These data make clinical study of recurrent pregnancy loss and its treatment difficult because very large groups of patients must be studied to demonstrate the effects of any proposed therapeutic intervention.
Etiology
Parental chromosomal abnormalities and thrombotic complications of the antiphospholipid antibody syndrome (APS) are the only undisputed causes of recurrent abortion. However, collectively these abnormalities account for less than 10% to 15% of recurrent pregnancy losses. Although the exact proportion of patients diagnosed with a particular abnormality may vary among the populations studied, other associations have been made with anatomic abnormalities (12%–16%), endocrine problems (17%–20%), infections (0.5%–5%), and immunologic factors, including those associated with the APS (20%–50%). Other miscellaneous factors have been implicated and account for approximately 10% of cases. Among women aged 35 or greater who experience recurrent pregnancy loss, spontaneous fetal chromosomal abnormalities are likely to be responsible for the vast majority of losses (8). Even after a thorough evaluation, the potential cause remains unexplained in about one-third to one-half of all cases of recurrent loss (Table 33.1) (3,6,9).
Table 33.1 Proposed Etiologies for Recurrent Spontaneous Abortion
The timing of fetal demise provides etiologic clues and its documentation is important in investigations into causes and treatments for recurrent pregnancy loss. The vast majority of preclinical and early clinical pregnancy losses are the result of de novo fetal aneuploidy (10). This is also thought to be the cause of anembryonic pregnancy losses, whereas pregnancy losses occurring after 10 weeks of fetal development are much less likely to derive from fetal aneuploidy. Pregnancy losses resulting from de novo fetal aneuploidy, whether early and undocumented or documented through evaluation of chromosomal content in fetal tissues, cloud the results of many published studies. Their presence or absence must be documented in all investigations on recurrent pregnancy loss patients and their potential as a confounding factor discussed. The timing of fetal demise and tissue chromosomal analysis of any collected fetal tissues should be carefully weighed when diagnostic and therapeutic investigations into causes of recurrent pregnancy loss are being considered.
Genetic Factors
The most common inborn parental chromosomal abnormalities contributing to recurrent abortion are balanced translocations (11–14), in which one parent carries an overall normal gene content, but has a piece of one chromosome inappropriately attached to another. Depending on the nature of the translocation (reciprocal or Robertsonian), the gametes produced by the translocation carrier will be normal (reciprocal only), balanced, or unbalanced for the translocated DNA. When fertilized by a chromosomally normal gamete, the resulting embryos may be chromosomally normal (reciprocal only) or may be balanced or unbalanced carriers of the translocation. Most gametes and embryos with abnormal chromosomal status will not survive. Of those that do, live offspring will either be carriers of a balanced translocation or, for Robertsonian translocations, be monosomic or trisomic for the translocated chromosomal DNA.
Among the possible chromosomal monosomies, only that of the X chromosome typically permits viable offspring. On careful examination, however, many of these offspring may, in fact, exhibit mosaicism. Embryonic chromosomal monosomy may be particularly prevalent among patients with histories of recurrent pregnancy loss who are undergoing in vitro fertilization (IVF) (15). Compared with monosomies, chromosomal trisomies (e.g., trisomy 13, 18, and 21) appear to be tolerated a bit more readily, although mosaicism also may be implicated with these abnormalities.
Neither family history alone nor a history of prior term births is sufficient to rule out a potential parental chromosomal abnormality. Whereas the frequency of detecting a parental chromosomal abnormality is inversely related to the number of previous spontaneous losses, the chance of detecting a parental chromosomal abnormality is increased among couples who have never experienced a live birth (13). Abnormalities also may be detected upon parental karyotype analysis of some couples with a history of spontaneous abortions interspersed with stillbirths and live births (with or without congenital anomalies). Ultimately the use of parental karyotyping as a screening modality to evaluate the structural chromosomal etiologies of recurrent pregnancy loss may become insufficient. Evidence now suggests that, in some cases, paternal chromosomal abnormalities may be isolated within a particular fertilizing spermatozoon (16,17). Aneuploid spermatozoa may be particularly motile (18). Other structural chromosome anomalies, such as inversions and insertions, may also contribute to recurrent abortion, as can chromosomal mosaicism and single gene defects. X-linked disorders uncommonly result in recurrent abortion of male rather than female offspring (19).
Thrombophilias
There is a great deal of interest in the role of inherited thrombophilias in recurrent pregnancy loss (20–22). This heterogeneous group of disorders increases venous or arterial thrombosis. Their associations with pregnancy loss remains controversial and is attributed to hypothetical alterations in placental growth and development, particularly to alterations in placental vascular development (23–28). Abnormal placental vascularization and inappropriate placental thrombosis would link these thrombophilic states to pregnancy loss. Although some thrombophilic states may be acquired, most are heritable. Those heritable thrombophilias most often linked with reference to recurrent pregnancy loss include activated protein C resistance associated with mutations in factor V, deficiencies in proteins C and S, mutations in prothrombin, and mutations in antithrombin III.
Like spontaneous pregnancy loss, inherited and combined inherited or acquired thrombophilias are also surprisingly common. Greater than 15% of whites carry an inherited thrombophilic mutation (21). The most common of these are the factor V Leiden mutation, a mutation in the promoter region of the prothrombin gene and mutations in the gene encoding methylene tetrahydrofolate reductase (MTHFR). These disorders are present in their heterozygous state in approximately 5%, 2% to 3%, and 11% to 15% of healthy white populations, respectively (22,29–31). These common mutations are associated with mild thrombotic risks. It remains controversial whether homozygous MTHFR mutations are associated with vascular disease at all (32). In contrast, more severe thrombophilic deficiencies, such as those of antithrombin and of protein S, are much less common in the general population. These epidemiologic data support the hypothesis that a selective genetic advantage may accompany carriage of common heritable thrombophilias. To this point, women with activated protein C resistance because of the factor V Leiden mutation have reduced blood loss at delivery and factor V Leiden carriage is reported to improve pregnancy rates in intracytoplasmic sperm injection or IVF, suggesting a positive role in implantation (33,34). It is important to note that the above epidemiology of factor V Leiden mutations is specific to white populations. Factor V Leiden and prothrombin gene mutations are rare in African and Asian populations, despite similar incidence of venous thromboembolic events (35–38). Protein C, protein S, and antithrombin mutations are the most important risk factors for venous thromboembolic events among many Chinese and other Asian populations (39). These ethnographic differences are important considerations when faced with decisions concerning diagnostic testing in patients with a history of recurrent fetal loss.
The proposed mechanistic basis for the association between adverse fetal outcomes and heritable thrombophilias has focused on impaired placental development and function, secondary to venous and/or arterial thrombosis at the maternal–fetal interface. These findings have been noted in the placentas of women with adverse fetal outcomes and known inherited thrombophilias and have been demonstrated in patients with similar outcomes, but lacking inherited thrombophilic risk (40–44). Discussions of placental thrombosis as causal in early pregnancy losses (<10 weeks gestation) are particularly contentious, citing an elegant series of experiments demonstrating that maternal blood flow into the intervillous spaces of the human placenta does not occur until approximately 10 weeks of gestation (45–48). Prior to establishment of intervillous circulation, nutrient transfer from maternal blood to fetal tissues appears to be dependent on transudation that, in turn, relies on flow through the uterine vasculature. This suggests that maternal or fetal thrombotic episodes in the developing placental vasculature could be equally devastating prior to or after the establishment of intervillous circulation near 10 weeks of gestation. Very early pregnancy losses (biochemical, anembryonic) and known aneuploid fetal losses are unlikely to be altered by the presence of, or treatment for, an underlying thrombophilic state.
The coagulation system relies on a complex cascade of prothrombotic enzymatic activations (often via serine proteases) in delicate balance with antithrombotic pathways. Although pregnancy is most simply described as prothrombotic, the alterations in the coagulation system associated with pregnancy may be described as a state of compensated disseminated intravascular coagulation (DIC) (49). Human hemochorial placentation is unique and inherently unstable. Placental development involves invasion into the maternal decidua and its vasculature and requires precise control of hemostasis and fibrinolysis. Delicate control mechanisms exist locally within the placenta and globally within the pregnant woman (50). Hormonal and related physiologic changes characteristic of pregnancy affect important components of the clotting cascade, the fibrinolytic cascade, and platelet physiology.
Figure 33.1 The clotting cascade. Physiologic clotting is initiated by endothelial cell damage or abnormal exposure of negatively charged phospholipids to serum and blood components. Procoagulant pathways in black are part of the clotting cascade and are prothrombotic. Both lead to activation of cascades of proteolytic enzymes and cleavage of clotting factors. The extrinsic and intrinsic pathways are initiated by distinct mechanisms. They merge at the activation of factor X to form the common pathway. For all coagulation factors, the subscript letter “a” denotes the activated form of the factor.
Clot formation can be initiated through two pathways, called the extrinsic and intrinsic clotting cascades (Fig. 33.1). Both respond to blood vessel damage and the release of tissue factor (TF).Tissue factor is a glycoprotein expressed on the surface of cells surrounding blood vessels. It is not expressed on the endothelium of the blood vessel itself, so exposure of blood to TF is a sensitive indicator of vascular damage. The extrinsic clotting cascade begins with the interaction of newly released TF with factor VII of the clotting cascade. The complex formed by TF and factor VII can either activate factor X directly or activate factor X via the intrinsic pathway. In the intrinsic pathway, the TF/factor VII complex activates factor IX to factor IXa (activated factor IX). Factor IXa then complexes with factor VIIIa. In combination, factors IXa and VIIIa activate factor X. Activation of factor XII after binding to negatively charged surfaces can also initiate the intrinsic pathway. Via this route, activated factor XII cleaves factor XI, generating factor XIa. Factor XIa can act as an alternate activator of factor IX. Extrinsic and intrinsic clotting cascades converge in the activation of factor X to factor Xa. Activated factor X (Xa) catalyzes the conversion of prothrombin (factor II) to thrombin (factor IIa). This conversion depends on the presence of activated factor V, which is factor Va. Thrombin, in turn, converts fibrinogen to fibrin, an essential building block for stable clot formation. Thrombin also activates factor XIII, which, in turn, crosslinks fibrin monomers and thereby stabilizes the fibrin clot.
Figure 33.2 Physiologic mechanisms that counteract the clotting cascade. The procoagulant cascade is inhibited by several physiologic mechanisms. The balance between pro- and antithrombotic pathways determines the state of coagulability. Antithrombotic mechanisms include the action of antithrombin (AT) and of proteins C and S. The sites of inhibition by these substances are depicted by an “X.” Plasminogen activator inhibitors-1 and -2 (PAI-1 and PAI-2) indirectly inactivate plasmin. Plasmin plays an important role in the dissolution of coagulated blood. For all coagulation factors, the subscript letter “a” denotes the activated form of the factor. FSP, fibrin split products; FDP, fibrin degradation products.
To avoid uncontrolled thrombosis in response to tissue damage or alternate activation of the coagulation cascade, a number of antithrombotic control mechanisms are activated in conjunction with clot formation (Fig. 33.2). Important to this discussion are antithrombin (formerly antithrombin III), protein C, and protein S. Proteins C and S are vitamin K–dependent factors that are activated upon clot formation. Activation is initiated by complexes of thrombomodulin and thrombin at sites of endothelial damage. Complexes of activated protein C and S inactivate factors Va and VIIIa, thereby inhibiting their associated procoagulant activities. Antithrombin is a serine protease inhibitor that binds irreversibly to serine proteases. Proteases that bind antithrombin include factors IXa, Xa, XIa, and XIIa. Antithrombin also accelerates dissociation of factor VIIa/tissue factor complexes, thereby inhibiting intrinsic and extrinsic clotting pathways at their points of initiation. Finally, as its name suggests, antithrombin binds to and inhibits thrombin (factor IIa). Fibrinolysis also acts to delimit uncontrolled coagulation (Fig. 33.3). Mechanisms for fibrinolysis include cleavage of the fibrin clot by plasmin and the formation of fibrin degradation products (FDPs; or fibrin split products [FSPs]). Plasmin activity is, in turn, controlled by plasminogen activator inhibitors (e.g., PAI-1).
Figure 33.3 Alterations coagulation and fibrinolysis during normal pregnancy. Pregnancy is a state of hypercoagulability. Levels of factors VII, VIII, X, and XII are elevated throughout pregnancy, levels of factors II, V, and XIII rise in the first trimester, then return to normal values. The antithrombotic activity mediated by protein S decreases in pregnancy. The placenta produces plasminogen activator inhibitor-2 (PAI-2). For all coagulation factors, the subscript letter “a” denotes the activated form of the factor. FSP, fibrin split products; FDP, fibrin degradation products.
Prothrombotic changes associated with pregnancy include increases in the amounts and/or activities of factors in the clotting cascade and decreases in those counteracting clotting. The former includes pregnancy-associated elevations in factors VII, VIII, X, XII, von Willebrand’s factor, and fibrinogen levels (49,51,52). All rise throughout gestation. Factor II, factor V, and factor XIII levels also rise early in pregnancy, but return to normal levels after the first trimester (49,53). Normal pregnancy has been associated with the development of activated protein C resistance (acquired APCR, see below) via mechanisms that remain unclear (54). Changes in balancing antithrombotic control mechanisms during pregnancy also favor clot formation. The activities of protein C and antithrombin remain fairly constant during the course of pregnancy. Protein S activity significantly decreases in conjunction with pregnancy-induced increases in the production of C4b-binding protein, a complement factor-binding protein that complexes with protein S, making it unavailable for interaction with activated protein C. This increased binding does not fully explain the level of decrease in protein S activity during pregnancy (55).
Figure 33.4 Homocysteine metabolism. Dietary methionine is metabolized either to cysteine or back into methionine. Homocysteine, a prothrombotic metabolite, is an intermediate in this process. Conversion of homocysteine to methionine requires transfer of a methyl group from 5-methyltetrahydrofolate. The conversion of folate to 5-methyltetrahydrofolate is a multistep process requiring vitamin B2 as a cofactor for the enzyme, methylene tetrahydrofolate reductase (MTHFR). Vitamin B12 is a required cofactor for the enzyme methionine synthase. Vitamin B6 is also required for metabolism of sulfur containing amino acids such as methionine.
Fibrinolysis is impaired during pregnancy, with decreases in fibrinolytic activity beginning at approximately 11 to 15 weeks of gestation (49). A significant factor in this impairment is a marked decrease in plasmin activity, resulting from placental production of the plasmin inhibitor PAI-2 (56,57). In conjunction with these changes, however, FDP levels are seen to rise in pregnancy, beginning at approximately 20 weeks of gestation, and continue their rise throughout pregnancy (49,56). In normal pregnancy, platelet function and turnover is unchanged. In the third trimester, platelet number typically decreases as the result of increased platelet consumption. This benign gestational thrombocytopenia can reach levels less than 80 × 109/L (58). Taken together, pregnancy-associated alterations in the amounts and activities of prothrombotic clotting factors, anticoagulant control mechanisms, and fibrinolysis support the determination of human pregnancy as a state of compensated DIC. Although these changes reverse during the 4 to 6 weeks following delivery, the vascular damage associated with delivery is an additional significant risk factor for thrombosis, making the immediate postpartum period an important continuation of the prothrombotic state associated with pregnancy (49,58).
Circulating homocysteine is derived from dietary methionine. Homocysteine, in turn, is metabolized either into cystathionine or back into methionine (Fig. 33.4). The latter process involves the enzyme methionine synthase. Methionine synthase requires donation of a methyl group from 5-methyltetrahydrofolate to produce methionine, and the enzyme MTHFR is involved in the production of 5-methyltetrahydrofolate from dietary folate sources (20). The nutritional supplements folic acid, vitamins B2, B6, and vitamin B12 are all required for proper metabolism of homocysteine; therefore, their deficiency is associated with acquired elevations in circulating homocysteine levels (21,29,59). Although heritable deficiencies in the enzymes required for metabolism of homocysteine have been described for the pathways leading to cystathionine formation and those involved in reconversion to methionine, mutations in MTHFR have received the most attention (20,59–61). Point mutations in MTHFR are surprisingly common, are associated with hyperhomocysteinemia, and are linked to thrombosis (22,29,59–61).
Those heritable thrombophilias most often linked to recurrent pregnancy loss include hyperhomocysteinemia, activated protein C resistance associated with mutations in factor V, deficiencies in proteins C and S, mutations in prothrombin, and mutations in antithrombin. These inherited disorders are mainly autosomal dominant and display a wide variation in prevalence and in the severity of morbidity associated with gene carriage. The latter two characteristics have direct reciprocal correlations in white populations. In agreement with general thrombotic risk data, carriage of combinations of two or more inherited thrombophilic defects has particularly strong association with adverse pregnancy outcome (22,24,30,62). Acquired thrombophilias associated with recurrent pregnancy loss include hyperhomocysteinemia and activated protein C resistance. The vast majority of the data linking thrombophilic states to recurrent fetal loss consist of small- to moderate-sized prevalence studies (62–70). Recent attempts to pool these data into meta-analyses have led to more informed recommendations on the testing of patients presenting with recurrent pregnancy loss (71–73). Taken together, these studies suggest that testing for the factor V Leiden mutation, protein S levels, prothrombin promoter mutations, homocysteine levels, and global activated protein C resistance is of use in white patients with a history of repetitive first or second trimester losses. These recommendations do not apply to patients who are nonwhite. Data directly linking hyperhomocysteinemia, folic acid, vitamin B12, and MTHFR mutations to recurrent pregnancy loss have been contradictory (41,43,60–62,65,66,68). Studies have evaluated pooled data from previous investigations (one via meta-analysis) and show these disorders to be linked to risk for recurrent pregnancy loss (72).
Anatomic Abnormalities
Anatomic abnormalities of both the uterine cervix and the uterine body have been associated with recurrent pregnancy loss (74,75). These anatomic causes may be either congenital or acquired.During development, the uterus forms via the apposition of a portion of bilateral hollow tubes called the müllerian ducts. The dissolution of the walls of these ducts along their site of apposition allows formation of the intrauterine cavity, the intracervical canal, and the upper vagina. Congenital uterine anomalies may, therefore, include incomplete müllerian duct fusion, incomplete septum resorption, and uterine cervical anomalies. Although the causes underlying many of the congenital anomalies of the female reproductive tract are unclear, it has been well documented that prenatal exposure to maternally ingested diethylstilbestrol (DES) results in complex congenital uterine, cervical, and vaginal changes.
Historically, all congenital reproductive tract abnormalities have been linked to both isolated spontaneous pregnancy loss and to recurrent pregnancy loss, although the presence of an intrauterine septum and prenatal exposure to DES demonstrate the strongest associations (76–78). Women with an intrauterine septum may have as high as a 60% risk for spontaneous abortion (79). Uterine septum–related losses most frequently occur during the second trimester (80). However, if an embryo implants into the poorly developed endometrium overlying the uterine septum, abnormal placentation and resultant first trimester losses may occur (81). The most common uterine congenital anomaly associated with in utero DES exposure is hypoplasia, which may contribute to first- or second-trimester spontaneous abortions, incompetent cervix, and premature labor (82,83). Congenital anomalies of the uterine arteries also may contribute to pregnancy loss via adverse alterations in blood flow to the implanted blastocyst and developing placenta (84).
Acquired anatomic anomalies have likewise been linked to both isolated and recurrent pregnancy losses. These abnormalities include such disparate conditions as intrauterine adhesions, uterine fibroids, and endometrial polyps. Endometrium that develops over an intrauterine synechiae or over a fibroid that impinges in the intrauterine cavity (submucous) may be inadequately vascularized (85). This may promote abnormal placentation for any embryo attempting to implant over such lesions. Although data supporting these concepts are limited, this abnormal placentation may lead to spontaneous pregnancy loss. Less clear is the association between intramural fibroids and recurrent pregnancy loss, but it is suggested that large (>5 cm) intramural fibroids are associated with pregnancy loss and that removal improves outcomes (78,86) (see Chapter 15).
Endocrine Abnormalities
The endocrinology of normal pregnancy is complex. Because spontaneous pregnancy is critically dependent on appropriately timed endocrinologic changes of the menstrual cycle, it is not surprising that those endocrine abnormalities that ultimately alter pregnancy maintenance may mediate their effects during the follicular phase of the cycle in which conception occurs, or even earlier.Modifications in follicular development and ovulation, in turn, may be reflected in abnormalities of blastocyst transport and development, alterations in uterine receptivity to the implanting blastocyst, and improper functioning of the corpus luteum. Beginning with ovulation and lasting until approximately 7 to 9 weeks of gestation, maintenance of early pregnancy depends on the production of progesterone by the corpus luteum. Normal pregnancies are characterized by a luteal–placental shift at about 7 to 9 weeks gestation, during which the developing placental trophoblast cells take over progesterone production and pregnancy maintenance (87). Spontaneous pregnancy losses occurring before 10 weeks of gestation may result from a number of alterations in normal progesterone production or utilization. These include failure of the corpus luteum to produce sufficient quantities of progesterone, impaired delivery of progesterone to the uterus, or inappropriate utilization of progesterone by the uterine decidua. Pregnancy failures may also occur near the time of the expected luteal–placental shift if the trophoblast is unable to produce biologically active progesterone following demise of the corpus luteum.
Endocrinologic factors associated with recurrent abortion include luteal phase insufficiency, diabetes mellitus, hypersecretion of luteinizing hormone (LH), thyroid disease, and, potentially, insulin resistance and polycystic ovarian syndrome, hyperprolactinemia and decreased ovarian reserve. Luteal phase insufficiency or luteal phase defects (LPD) are characterized by inadequate luteal milestones and most likely relate to adverse pregnancy outcome via inadequate or improperly timed endometrial development at potential implantation sites. An elegant description of abnormalities at the site of implantation, which may be responsible for some cases of recurrent pregnancy loss, describes impaired decidualization of the endometrium as a mechanism for natural selection of human embryos (88). LPD has many causes, some of which are associated with hypersecretion of luteinizing hormone. Although the mechanism underlying the association of elevated LH levels with recurrent pregnancy loss is incompletely understood, abnormal LH secretion may have direct effects on the developing oocyte (premature aging), on the endometrium (dyssynchronous maturation), or both. Many patients with elevated LH levels also display physical, endocrinologic, and metabolic characteristics of polycystic ovarian syndrome (PCOS). Some studies report ovarian radiologic evidence of PCOS in as many as 40% to 80% of recurrent pregnancy loss patients (89,90). In addition to inappropriately elevated LH levels, PCOS patients are frequently obese and often have elevated circulating androgen levels. Although not undisputed, both changes have been linked to recurrent pregnancy loss, and elevated androgen levels have been shown to adversely affect markers of uterine receptivity in women with a history of recurrent pregnancy loss (89–92).
Many women with PCOS have metabolic alterations in glycemic control characterized by insulin resistance. This too may be directly or indirectly related to adverse pregnancy outcome, and it may explain increases in the rate of spontaneous pregnancy loss among women with type 2 diabetes mellitus (93). Women with overt insulin-dependent diabetes mellitus (IDDM) appear to exhibit a threshold of pregestational glycemic control above which spontaneous pregnancy loss is increased (94,95). In fact, hyperglycemia has now been directly linked to embryonic damage (96). In cases of advanced IDDM with accompanying vascular complications, compromised blood flow to the uterus may be mechanistically involved in subsequent pregnancy loss.
Patients with thyroid disease often have concomitant reproductive abnormalities, including ovulatory dysfunction and luteal phase defects. In addition, the metabolic demands of early pregnancy mandate an increased requirement for thyroid hormones. It is therefore not surprising that hypothyroidism has been associated with isolated spontaneous pregnancy loss and with recurrent pregnancy loss (97). The definition of hypothyroidism is itself now under scrutiny with many investigators suggesting that cutoff thyroid-stimulating hormone (TSH) values during pregnancy should be less than 2.5 mIU/mL (98). Others have suggested even lower TSH cutoff values (99). Although it has long been debated whether clinically euthyroid patients with antithyroid antibodies have higher rates of miscarriage and recurrent pregnancy loss, thyroid hormone supplementation was shown to reduce miscarriage in infertility patients with positive antithyroid antibodies undergoing IVF (100–106). The mechanism for an association between antithyroid antibody positivity and recurrent pregnancy loss remains unclear; however, these antibodies could be markers of more generalized autoimmunity or may predict an impaired ability of the thyroid gland to respond to the demands of pregnancy.
Two additional endocrinologic abnormalities have been linked with recurrent pregnancy loss, although support for these associations and their mechanistic pathways remains shrouded in controversy. The relationship of hyperprolactinemia with recurrent pregnancy loss continues to be debated. Animal models suggest that elevated prolactin levels may adversely affect corpus luteal function; however, this concept is not well supported in humans (107,108). Some have suggested that elevated prolactin levels may promote pregnancy wastage via direct effects on the endometrium or indirect immunomodulatory mechanisms (88,109). Most recently, attempts have been made to correlate markers of ovarian reserve (day 3 follicle-stimulating hormone, day 3 estradiol, response to the clomiphene challenge test) with recurrent pregnancy loss (89,110,111). At present, no consensus exists concerning this potential association.
Maternal Infection
The association of infection with recurrent abortion is among the most controversial and poorly explored of the potential causes for pregnancy loss. Reproductive tract infection with bacterial, viral, parasitic, zoonotic, and fungal organisms have all been linked theoretically to pregnancy loss; however, mycoplasma, ureaplasma, chlamydia, and β-streptococcus are the most commonly studied pathogens (112,113). More recent data have directly addressed the roles of some of these proposed organisms in recurrent pregnancy loss. One prospective comparison trial involving 70 recurrent pregnancy loss patients reported no elevations in any markers for present or past infection with Chlamydia trachomatis when compared with controls (114). In contrast, a very large, prospective trial demonstrated a link between the detection of bacterial vaginosis and a history of second trimester pregnancy loss among 500 recurrent pregnancy loss patients (115). The risk of bacterial vaginosis detection was also positively correlated with cigarette smoking in this study.
The etiologic mechanism linking specific organisms to either isolated or recurrent pregnancy loss remains unclear and must certainly differ among infectious organisms. Certain viral organisms, such as herpes simplex virus (HSV) and human cytomegalovirus (HCMV) can directly infect the placenta and fetus (116,117). The resulting villitis and related tissue destruction may lead to pregnancy disruption. Another theoretic possibility warranting study is that infection-associated early pregnancy loss may result from immunologic activation in response to pathologic organisms. A large body of evidence supports the role of this mechanism in adverse events later in gestation, such as intrauterine growth restriction, premature rupture of membranes, and preterm birth (118,119). Alternatively, mechanisms that protect the fetus from autoimmune rejection also may protect virally infected placental cells from recognition and clearance. This could potentially promote periods of unfettered infectious growth for some of the pathogenic organisms gaining entry to the reproductive tract (120).
Immunologic Phenomena
During the past decade, there has been extensive information published concerning the possible immunologic causes and treatments of recurrent pregnancy loss. There is a lack of consensus as to the mechanisms and the impact of therapeutic intervention because the detection of a therapeutic effect is difficult in the absence of very large studies. This situation reflects the fact that many recurrent pregnancy loss patients present after their index pregnancy has expired but prior to its being expelled. In these cases, the physiologic immune reaction to the presence of nonviable tissue may mask any alternative, underlying immune causes for the demise itself. Finally, it is very likely that there are a wide variety of immune alterations that may result in the same end point—isolated or recurrent pregnancy loss. This latter theory is certainly supported by a now classic review article that lists 10 fairly well-supported immune mechanisms that are each potentially important in pregnancy maintenance (121) (Tables 33.1 and 33.2).
Table 33.2 Concepts in Reproductive Immunology
Before launching into the most commonly accepted causes of immune-mediated pregnancy loss, a brief review of some of the important concepts in basic immunology is warranted. Although these descriptions are presented in general terms, and are further defined in Chapter 6, they should serve as useful reference for the ensuing information.
Immune responses classically are divided into innate and acquired responses. Innate responses represent the body’s first line of defense against pathogenic invasion. They are rapid and are not antigen specific. Cell types and mechanisms typically considered vital to innate immunity include complement activation, phagocytosis by macrophage, and lysis by natural killer (NK) and natural killer T (NKT) cells and possibly by TCR γδ+ T cells (see below). Acquired immune responses, in contrast, are antigen specific and are largely mediated by T cells and B cells. Acquired responses can be further divided into primary (response associated with initial antigen contact) and secondary (rapid and powerful amnestic responses associated with subsequent contact to the same antigen).
Antigen specificity is generally regulated by two sets of genes in the major histocompatibility complex (MHC), located on chromosome 6 in humans. MHC class I molecules (HLA-A, -B, and -C) are present on the surface of nearly every cell in the human body and are important in defense against intracellular pathogens, such as viral infection and oncogenic transformation. MHC class I molecules act as important ligands for both the T-cell receptor on CD8+ cytotoxic/suppressor T cells and for a variety of receptors on NK cells (122). MHC class II molecules (HLA-DR, HLA-DP, and HLA-DQ), in contrast, are present on the surface of a limited number of antigen-presenting cells, including dendritic cells, macrophage and monocytes, B cells, and tissue-specific cells such as the Langerhans cells in the skin. These molecules are important in defense against extracellular pathogens, such as bacterial invaders. The major ligand for MHC class II is the T-cell receptor on CD4+ T-helper cells.
One very important concept in immunology that has particular application to pregnancy is that of immune tolerance. The passage of bone marrow–derived T cells through the fetal thymus during early development has been well described. During this developmental interval, the T cells encounter a process termed thymic education. During thymic education, T cells that express either the CD4 or the CD8 coreceptor are chosen, and autoreactive cells are effectively eliminated. In short, this education promotes T-cell tolerance, allowing selection and survival only of those T cells that recognize non-self and will not react against self. Recently, a subpopulation of CD4+ T cells has been described that, like all activated lymphocytes, strongly express CD25 on their cell surface (123). These CD4, CD25+ cells are more specifically identified by the intracellular presence of the forkhead box P3 (Fox P3) transcription factor and have been called regulatory T lymphocytes (Treg cells). Treg cells, when activated by autoantigens, can suppress activated inflammatory cells. They secrete regulatory cytokines, including interleukin-10 (IL-10) and transforming growth factor-β (TGF-β) (123–125). They may have particular importance in avoidance of tissue destruction associated with inflammation, possibly with applications to tolerance. In an abortion-prone murine model, adoptive transfer of Treg cells from normal pregnant mice into abortion-prone animals prevented immune-mediated pregnancy wastage (126). In pregnant women, Treg cells suppress autologous peripheral blood mononuclear cell (PBMC) secretion of the inflammatory cytokine, interferon-γ (IFN-γ) when challenged by paternal or unrelated PBMCs (127).
These immunologic characteristics were thoroughly described and investigated for the immune effector cells populating the peripheral immune system. The peripheral immune system consists of the spleen and peripheral blood, and it is generally responsible for protection against blood-borne pathogens. Pathogens that enter the host via the extensive surface areas of the lacrimal ducts, respiratory system, gastrointestinal tract, mammary ducts, and genitourinary tract encounter a very distinct and important immune environment—that of the mucosal immune system. Although the mucosal immune system may be primarily responsible for the initial protection against most exogenous pathogens, an understanding of its immune characteristics lags far behind that of the peripheral immune system. Insight into the specific characteristics of immunity within the reproductive tract is even further limited.
Cellular Immune Mechanisms
Many of the immune theories surrounding the causes of isolated and recurrent spontaneous pregnancy losses have stemmed from attempts to define immunologic rules as they apply specifically to the mucosal reproductive tract. Four main questions summarize much of the theoretical thinking surrounding pregnancy maintenance and reproductive immunology:
1. Which immune cells populate the reproductive tract, particularly at implantation sites?
2. How do these cells arrive at this mucosal immune site and are they educated in the same way as those populating the periphery?
3. How do the characteristics of antigen presentation differ at the maternal–fetal interface?
4. What regulatory mechanisms specifically affect reproductive tract immune cells?
Resident Cells
Immune cells populating the reproductive tract exhibit many characteristics that distinguish them from their peripheral counterparts. In particular, the human endometrium is populated by T cells, macrophage, and NK-like cells, but very few B cells are present. The relative proportions of these resident cells vary with the menstrual cycle and change dramatically during early pregnancy. In fact, surrounding the time of implantation, one particular cell type comprises between 70% to 80% of the total endometrial lymphocyte populations (128,129). This cell type is called a variety of names, including decidual granular lymphocytes (DGLs), large granular lymphocytes (LGLs), and decidual NK cells. This heterogeneity of names reflects the fact that this particular cell type differs from similar cells isolated from the periphery, although most believe it to be an NK cell variant. While the majority of peripheral NK cells have low cell surface expression of CD56 (CD56dim) and express high levels of CD16, the immunoglobulin receptor responsible for NK-mediated, antibody-dependent cellular cytotoxicity, those in the uterine decidua and at the placental implantation site, are largely CD56bright and CD16dim or CD16− (130). If these unusual endometrial cells are considered NK cells, the implantation site represents the largest accumulation of NK cells in any state of human health or disease. The true function of these cells remains unclear, but their remarkable abundance at the maternal–fetal interface compels further study. These decidual NK cells display fairly poor cytotoxic function but are robust cytokine secretors (131,132). The balance of activating and inhibitory receptors expressed on their cell surfaces determines their ultimate killing versus secretion patterns (133,134). Increases in killer-type activating receptors in comparison to inhibitory receptors were found among patients with a history of recurrent pregnancy loss (135,136). Other immune cells have been described in the periphery as having the characteristics of both NK cells and T cells. These NKT cells demonstrated a role in pregnancy loss in animal models (137). They are present in the decidua in humans and may play an important immunoregulatory role at this site (138).
In the peripheral immune compartment, the vast majority of T cells express a T-cell receptor comprised of an αβ heterodimer (TCRαβ+). In addition to TCRαβ+ T cells, the human reproductive tract also is populated by a subset of T cells with a distinctive T-cell receptor comprised of the γδ heterodimer (TCRγδ+), and the numbers of these cells increases in early pregnancy (139–141). TCRγδ+ T cells appear to fulfill functions quite distinct from their αβ+ counterparts; functions that may include direct, non-MHC restricted recognition of antigens within tissues (142). TCRγδ+ T cells may fill a protective niche that is either missed or poorly covered by B cells and TCRαβ+ T cells. The role and importance of TCRγδ+ cells in the reproductive tract and, more particularly, in pregnancy maintenance deserves further attention.
Treg cells are also of the “suppressor” functional phenotype. In pregnant mice and women, these specialized CD4+ cells are systemically expanded in an alloantigen independent fashion and can suppress adverse maternal responses to the fetus (143) and to self (144).
The human decidua contains characteristic immune effector cells. Most investigations into whether alterations in these cells (including T cells, decidual NK cells, and NKT cells) determine pregnancy outcome are hampered by insufficient patient numbers to allow meaningful conclusions. These immune cell populations are reported to be altered in recurrent pregnancy loss patients but not in patients experiencing isolated spontaneous pregnancy losses (141,145–147).
Immune Cell Education and Homing to the Reproductive Tract
The implanting fetus represents the most common model of allograft acceptance. How the maternal immune system avoids rejection of the implanting fetus in an uncomplicated pregnancy invokes the presence of some manifestation of immune tolerance. This, in turn, begs the questions of how the resident decidual immune effector cells are selected and educated, how they home to reproductive sites, and how they are maintained once they reach this destination. Animal studies have suggested that the rules for selection and maintenance of these cells, in terms of their requirement for MHC and their education within the thymus, may be distinct from those governing either peripheral immune cells or cells within other mucosal sites, including the intestine (148). It appears the human reproductive tract displays similar characteristics—the immunophenotypes of immune cells populating the human reproductive tract are distinct from both the periphery and from other mucosal sites (149,150). The education of TCRγδ+ cells populating epithelial sites may occur outside the thymus and might involve mechanisms that substitute for or modify interaction with MHC (141,151). The development of MHC specificity among NK cells is presently being carefully dissected in animal models with the hope that these investigations will shed light on similar processes in humans and, more specifically, on the selection and maintenance characteristics of decidual NK cells (133,134,152,153).
It is becoming increasingly evident that the cells populating mucosal immune tissues select these sites through interactions between cell surface molecules on the immune cell (integrins) and cell surface molecules on the endothelial cells of blood vessels within the mucosal tissues (e.g., selectins). This cellular recruitment process, called homing, has been most thoroughly described for the intestine (154,155). Both murine and human reproductive tract tissues express these integrin or vascular ligand pairs (155–157). The extension of these findings to pregnancy maintenance will be useful (158,159). Solving the mechanisms of selection, education, and maintenance of reproductive tract immune effector cells is of paramount importance. Until we understand these vital processes in the normal state, we cannot define the effects that alterations will have on human disease nor can we develop therapeutic interventions.
Antigen Presentation at the Maternal–Fetal Interface
Historically, it was proposed that one method by which the implanting trophoblastic allograft potentially could avoid immune detection by the maternal host would be by making itself antigenically invisible. It could downregulate its expression of the MHC-encoded transplantation antigens (some of which would be of paternal origin) and thereby avoid recognition as non-self. Although current knowledge of immunology renders this theory obsolete, the implanting fetus does utilize this strategy to some extent (160). It is certainly true that placental trophoblast cells do not express MHC class II molecules (161,162).
Unlike nearly every other cell in the human body, trophoblast cells do not express the classical MHC class I transplantation antigens HLA-A and -B. Rather, a subpopulation of placental cells, specifically the extravillous cytotrophoblast cells, express the classical MHC class I HLA-C products, and the nonclassical HLA-E and -G products (120,163–167). These extravillous cytotrophoblast cells are of particular interest because they are characterized by remarkable invasive potential (168,169). These cells move from the tips of the anchoring villae of the human placenta, invading deeply into the maternal decidua, and can replace cells within the walls of decidual arterial vessels (168–170). Although the invasive characteristics of extravillous cytotrophoblast may reflect non-MHC–related mechanisms, including well-described integrin switching, the intimate contact of these fetal-derived cells with maternal immune effector cells certainly exposes the fetus to recognition as nonself (171).
It is not known why all placental cells downregulate expression of HLA-A and -B, whereas invasive extravillous cytotrophoblast express HLA-C, -E, and -G. This area of investigation is ripe with hypotheses and study. Because NK cells of the innate immune system recognize and kill cells that express no MHC, the complete downregulation of MHC should cause trophoblast cells to act as targets for those NK cells that are pervasive at sites of implantation (134,160). In addition to possible protection from direct NK cell–mediated killing, the expression of HLA-C, -E, and -G by trophoblast cells may serve a variety of alternate purposes. NK cell receptor-mediated interactions with extravillous cytotrophoblast MHC products modulate cytokine expression profiles at the maternal–fetal interface (131,132). MHC expression aids in decidual and vascular invasion by the trophoblast, an activity essential for proper placental development (172). Whereas definitive correlations between placental MHC class I expression patterns and recurrent pregnancy loss have not been reported, trophoblast expression of HLA-G was linked to other disorders of placental invasion, such as preeclampsia (172,173). Genetic mutations at the HLA-G locus have also been linked to recurrent pregnancy loss in some, but not all studies (174–177). Finally, soluble or secreted trophoblast MHC products may aid in the development of maternal immune tolerance toward the placenta (178). Soluble HLA-G was shown to suppress T lymphocyte and NK cell function and to induce the expansion of Treg cells in humans (179).
Aberrant expression of class II MHC determinants, or enhanced expression of MHC class I on syncytiotrophoblast occurring in response to IFN-γ (180) could mediate pregnancy loss by enhancing cytotoxic T-cell attack (181). This theory appears unlikely, because the expression of classical MHC antigens does not seem to be induced on aborted tissues from women experiencing one or more pregnancy losses (181). Finally, MHC class II genotypes appear to affect susceptibility to a variety of diseases, including diabetes and other autoimmune diseases. A similar link between MHC class II typing and adverse pregnancy outcome was reported for recurrent pregnancy loss(182,183).
Regulation of Decidual Immune Cells
The characteristics of the interactions between decidual immune effector cells and the implanting fetus may be determined by factors other than those already mentioned. Local regulation of the cells that populate the human decidua will further modify the effects of selection, maintenance, and homing, as well as the distinctive characteristics of antigen presentation at the maternal–fetal interface. As might be predicted, these regulatory effects are often targets for investigative efforts, because they may offer more direct insight into potential therapies for immune-mediated disorders of pregnancy maintenance. Three such regulatory mechanisms will be discussed here: (i) alterations in T-helper cell phenotypes, (ii) reproductive hormones and immunosuppression, and (iii) tryptophan metabolism.
As discussed in Chapter 6, antigen-stimulated immune responses involving CD4+ T cells can be divided into two major classes: T helper 1 (TH1) responses and T helper 2 (TH2) responses. This subclassification may be overly simple, but it has been useful in broadly defining types of immune responses based on the characteristics of the CD4+ cells present, as well as their associated cytokines. The production of these responses rests on the environment in which relatively undifferentiated CD4+ TH0 cells become differentiated. Thus, TH0 cells exposed to IFN-γ become TH1-type cells, and those exposed to IL-4 become TH2-type cells (184). TH1 responses are associated with inflammation and primarily involve IFN-γ and IL-12, as well as IL-2, and tumor necrosis factor-β (TNF-β). TH2 cells responses are associated with antibody production and the cytokines IL-10, IL-4, IL-5, and IL-6 (184–186). Although TNF-α can be secreted by both TH1 and TH2 cells, it is most often a characteristic of TH1 response (187,188). A reciprocal regulating relationship exists between TH1 and TH2 cells and cytokines, with one response supporting its own persistence while averting conversion to the other (189–191).
One additional T-helper cell subset, TH17 cells, has been recently distinguished, although many of their proinflammatory effects were previously attributed to TH1 cells (192). TH17 cells preferentially produce IL-17 family cytokines (including IL-17A and IL-17F), which upregulate stromal IL-8 and IL-6 and cause local neutrophilic inflammation. These cells are important in sustaining the inflammatory response and are closely associated with several autoimmune diseases (193).
Extending these immune regulatory phenomena to pregnancy, the type of CD4+ cellular response to the implanting fetus is controlled not only by the types of cells (e.g., T-helper cells) in the decidua, but also by the cytokine environment at the maternal–fetal interface. As mentioned previously, the human endometrium and decidua are replete with immune and inflammatory cells capable of cytokine secretion (194–196). Cytokines may affect reproductive events either directly or indirectly, depending on the specific cytokines secreted, their concentrations, and the differentiation stage of potential reproductive target tissues. It is well documented that TH1-type cytokines can be harmful to an implanting embryo (197,198). Further, most agree that some patients with recurrent pregnancy loss exhibit a dysregulation of their T-helper cellular immune response to antigens at the site of implantation, with typical shifts toward TH1 inflammatory responses (199,200). Depending on the individual series, 60% to 80% of nonpregnant women with a history of otherwise unexplained recurrent spontaneous abortion have been found to have evidence of abnormal in vitro TH1 cellular immune responses. Fewer than 3% of women with normal reproductive histories demonstrate these responses (199,201). Rather, most women with normal pregnancies have a TH2 immune response to trophoblast antigens (199). It has only been recently that the TH17 concept has been applied to pregnancy (202). In humans, a single study demonstrates an increase in the number of TH17 cells in the decidua and peripheral blood of women with otherwise unexplained recurrent pregnancy loss (203). Mechanistically, a dysregulation of TH17 cell control by Treg cells may lead to adverse pregnancy outcomes (204).
Methods for the documentation of cytokine dysregulation among recurrent pregnancy loss patients also varies among investigators; some groups have confirmed this abnormality within the endometrium or among immune cells isolated from the decidua of these patients (205–208). Others use peripheral blood lymphocytes (PBLs) from women with a history of recurrent pregnancy loss and stimulate them in vitrowith trophoblast antigens (199,209). One study documented aberrant cytokine secretion when PBLs from recurrent pregnancy loss patients were stimulated in vitro by HLA-G bearing cells, whereas another study demonstrated that decidual and peripheral immune cells exhibit a shift toward the TH2 phenotype when exposed to HLA-G (210,211). Whether peripheral cytokine levels reflect T-helper cell dysregulation at the maternal–fetal interface and whether this dysregulation affects peripheral as well as local immune response during pregnancy remains controversial (212,213). Finally, as with all immune theories, there seems to be significant redundancy in the necessity for particular cytokines and soluble immunoregulatory factors at the site of implantation. To date, animal models with directed gene deletions have shown few of these factors to be absolutely essential to pregnancy maintenance (e.g., leukemia inhibitory factor [LIF]) (214,215).
Although many mechanisms are aimed at avoiding maternal immune recognition of the implanting fetus, research in both humans and animals indicates that immune responses to fetal antigens can be detected (216–218). Thus, the regulation of this response at the maternal–fetal interface may be critical. The concept that successful pregnancy requires some form of generalized suppression of maternal immune response is supported by reports that failure to downregulate maternal responses to recall antigens, such as tetanus toxoid and influenza, is associated with poor pregnancy outcome among recurrent pregnancy loss patients (219). Treg cells appear important in this respect (see above). So too do reproductive hormones. Reproductive hormones have dramatic effects on peripheral cell–mediated immunity, as demonstrated by well-documented and notable gender differences in immune responsiveness (220). The levels of these potentially immunosuppressive hormones are quite elevated in pregnant women. The fact that the levels of these hormones at the maternal–fetal interface may be far above those in the maternal circulation during pregnancy may explain an apparent inconsistency: overall immune responsiveness during pregnancy appears to change little, while local suppression at the maternal–fetal interface may be vital (221).
It has been suggested that the immunosuppressive effects of progesterone within the reproductive tract are at least partially responsible for the maintenance of the semiallogeneic implanting fetus(222). In vitro studies have shown that progesterone mediates its suppression of T-cell effector function by altering membrane-resident potassium channels and cell membrane depolarization. This action, in turn, affects intracellular calcium signaling cascades and gene expression and may be mediated by nonclassical steroid receptors or may not involve a receptor at all (223–225). Progesterone-mediated changes in T-cell gene expression have been associated with the development of TH2-type T-helper cell responses and with increased LIF expression (208,226). Because a shift in the intrauterine immune environment from TH2 to TH1 has been linked with early spontaneous pregnancy loss, the elevated intrauterine concentrations of progesterone characteristic of early pregnancy may promote an immune environment favoring pregnancy maintenance (199,208). To this point, in vitro evidence indicates that progesterone can inhibit mitogen-induced proliferation of and cytokine secretion by CD8+ T cells and can alter the expression of a transcription factor that drives the development of TH1 cells (227,228).
Levels of estrogen also rise dramatically during pregnancy, and attention has focused on the role of estrogen in immune modulation. A group of animal studies showed that estrogens improve immune responses in males after significant trauma and hemorrhage, suppress cell-mediated immunity after thermal injury, and protect against chronic renal allograft rejection (229–231). In vitro, estrogens appear to downregulate delayed-type hypersensitivity (DTH) reactions and promote the development of TH2-type immune responses, particularly at the elevated estrogen concentrations typical of pregnancy (232,233).
One additional regulatory mechanism proposed for the induction of maternal tolerance to the fetal allograft involves the amino acid tryptophan and its catabolizing enzyme indolamine 2,3 dioxygenase (IDO). The IDO hypothesis of tolerance in pregnancy rests on data that indicate that T cells need tryptophan for activation and proliferation (234), and that local alterations in tryptophan metabolism at the maternal–fetal interface could either activate or fail to suppress maternal antifetal immunoreactivity (235). Studies in mice have shown that the inhibition of IDO leads to loss of allogeneic, but not syngeneic, fetuses, and that this effect is mediated by lymphocytes (236). Further support lies in studies demonstrating that hamsters fed diets high in tryptophan have increased rates of fetal wastage (237). Extending this theory to humans requires further investigation. However, the demonstration of IDO expression in human uterine decidua, and the documentation of alterations in serum tryptophan levels with increasing gestational age during human pregnancy both support further interest in this potential local immunoregulatory mechanism (238,239).
Endometriosis is the growth of both endometrial glands and stroma outside of the intrauterine cavity. Although associations between the development of endometriosis and immunologic abnormalities are now being defined, the link between endometriosis and recurrent pregnancy loss remains contentious (240,241). The occurrence of recurrent pregnancy loss in the presence of endometriosis certainly would involve the interaction of complex mechanisms, some of which may involve cellular or humoral immune dysfunction (242,243).
Humoral Immune Mechanisms
Humoral responses to pregnancy-specific antigens exist, and patients with recurrent pregnancy loss can display altered humoral responses to endometrial and trophoblast antigens (Table 33.2) (199,244). Nevertheless, most literature surrounding humoral immune responses and recurrent pregnancy loss focus on organ nonspecific autoantibodies associated with the antiphospholipid antibody syndrome (APS). Historically, these immunoglobulin-G (IgG) and IgM antibodies were considered as directed against negatively charged phospholipids. Those phospholipids most often implicated in recurrent pregnancy loss are cardiolipin and phosphatidylserine. However, antiphospholipid antibodies often are directed against a protein cofactor, β2 glycoprotein 1, which assists antibody association with the phospholipid (245–249). Antiphospholipid antibodies were originally characterized by prolonged phospholipid-dependent coagulation tests in vitro (activated partial thromboplastin time [aPTT], Russell Viper Venom time) and by thrombosis in vivo. The association of these antiphospholipid antibodies with thrombotic complications has been termed the antiphospholipid syndrome, and although many of these complications are systemic, some are pregnancy specific—spontaneous abortion, stillbirth, intrauterine growth retardation, and preeclampsia (250,251). A reassessment of the criteria used to diagnose APS resulted in additions to the prior Sapporo criteria for diagnosis of APS and continues to include adverse pregnancy outcomes. These criteria, which have been validated clinically, are as follows (251–253).
For a patient to be diagnosed with antiphospholipid antibody syndrome, one or more clinical and one or more laboratory criteria must be present:
Clinical
1. One or more confirmed episode of vascular thrombosis of any type:
• Venous
• Arterial
• Small vessel
2. Pregnancy complications:
• Three or more consecutive spontaneous pregnancy losses at less than 10 weeks of gestation with exclusion of maternal anatomic and hormonal abnormalities and exclusion of paternal and maternal chromosomal abnormalities
• One or more unexplained deaths of a morphologically normal fetus at or beyond 10 weeks of gestation (normal fetal morphology documented by ultrasound or direct examination of the fetus)
• One or more premature births of a morphologically normal neonate at or before 34 weeks of gestation secondary to severe preeclampsia or placental insufficiency
Laboratory
Testing must be positive on two or more occasions with evaluations 12 or more weeksapart:
1. Positive plasma levels of anticardiolipin antibodies of the IgG or IgM isotype at medium to high levels
2. Positive plasma levels of lupus anticoagulant
3. Anti-β2 glycoprotein-1 antibodies of the IgG or IgM isotype in titers greater than the 99th percentile
The presence of antiphospholipid antibodies (anticardiolipin or lupus anticoagulant) and anti-β2 glycoprotein-1 antibodies during pregnancy is a major risk factor for an adverse pregnancy outcome (245,246,254). In a large series of couples with recurrent abortion, the incidence of the antiphospholipid syndrome was between 3% and 5% (112). The presence of anticardiolipin antibodies among patients with known systemic lupus erythematosus portends less favorable pregnancy outcomes (255).
A number of mechanisms have been proposed by which antiphospholipid antibodies might mediate pregnancy loss (256). Antibodies against phospholipids could increase thromboxane and decrease prostacyclin synthesis within placental vessels. The resultant prothrombotic environment could promote vascular constriction, platelet adhesion, and placental infarction (257–259). Alternatively, in vitroevidence from trophoblast cell lines indicates that IgM action against phosphatidylserine inhibits formation of syncytial trophoblast (260). Syncytialization is required for proper placental function. One study demonstrated that both extravillous cytotrophoblast and syncytiotrophoblast cells synthesize β2 glycoprotein-1, the essential cofactor for antiphospholipid antibody binding (261). Although it gives insight into pathophysiology, the prognostic value of serum levels of specific antibodies against β2 glycoprotein-1 with respect to pregnancy outcome among recurrent pregnancy loss patients is contentious and may be poorer than that of standard anticardiolipin antibodies (262–264). Some have proposed that sera from antibody positive recurrent pregnancy loss patients is particularly adept at inhibiting trophoblast adhesion to endothelial cells in vitro (265). Others noted rapid development of atherosclerosis in the decidual spiral arteries of patients who test positive for antiphospholipid antibodies (266). Finally, still others have demonstrated that levels of the placental antithrombotic molecule—annexin V—are reduced within the placental villa from those women with recurrent pregnancy loss who are antiphospholipid antibody positive (267). However, placental pathologic evidence supporting causal involvement of the antiphospholipid antibody syndrome in pregnancy loss often is equivocal. The characteristic lesions for this syndrome (placental infarction, abruption, and hemorrhage) are typically missing in women with antiphospholipid antibodies, and these same pathologic lesions can be found in placentae from women with recurrent abortion who do not have biochemical evidence of antiphospholipid antibodies (256,268–270).
One additional group of autoantibodies that have been linked to recurrent pregnancy loss is the antithyroid antibodies (ATA). Although the data remain somewhat controversial, several investigators demonstrated an increased prevalence of these antibodies among women with a history of recurrent pregnancy loss, even in the absence of thyroid endocrinologic abnormalities (98–199,102,103,271–273).
Other antibody-mediated mechanisms for recurrent abortion have been proposed, including antisperm and antitrophoblast antibodies, as well as blocking antibody deficiency. Although each hypothesis has minimal relevance to recurrent pregnancy loss, their discussion is warranted because therapies aimed at these disorders persist. Historically, the blocking antibody deficiency hypothesis has received the most attention (112,181). This hypothesis is based on a supposition that blocking factors (presumably antibodies) were required to prevent a maternal, cell-mediated, antifetal immune response that was believed to occur in all pregnancies. It was therefore proposed that, in the absence of these blocking antibodies, abortion occurred (273). This supposition was not consistently substantiated (274,275). For instance, maternal hyporesponsiveness in mixed lymphocyte culture with paternal stimulator cells was originally proposed to identify women with deficient blocking activity (273). Investigations based on this type of testing were continued by those who proposed that parental HLA sharing resulted in a predisposition to blocking antibody deficiency (276,277). These reports were of limited sample size, were retrospective in nature, and lacked population-based controls. One prospective, population-based control study conclusively demonstrated that HLA heterogeneity was not essential for successful pregnancy (278). However, follow-up studies showed that, in the exceedingly rare case of complete sharing of the entire HLA region, spontaneous pregnancy losses do increase (279). This particular 10-year prospective trial concluded that HLA typing is of no use in outbred populations, because only isolated and significantly inbred populations have such HLA homogeneity. Further evidence refuting the blocking antibody hypothesis for recurrent abortion comes from reports of successful pregnancies among women who do not produce serum factors capable of mixed lymphocyte culture inhibition and also among women who do not produce antipaternal cytotoxic antibodies (273,274). Those mixed lymphocyte culture results that demonstrate hyporesponsiveness in some recurrent pregnancy loss patients are now believed to represent the effect of the pregnancy loss rather than the cause of recurrent abortion (217,273–275).
One final theory that emerged from the blocking antibody investigations involved a novel HLA-linked alloantigen system. The finding that polyclonal rabbit antisera could recognize both lymphocytes and trophoblast cells suggested the existence of trophoblast–lymphocyte cross-reactive alloantigens (called TLX) (280). These TLX were, in turn, linked to maternal blocking antibody deficiency and recurrent pregnancy loss. The TLX hypothesis only has historical relevance. The theory was invalidated when TLX was found to be identical to CD46, a complement receptor that is thought to protect the placenta from complement-mediated attack (281). CD46 was not a novel alloantigen. It can be found on a wide variety of cells, thus explaining the cross-reactive nature of the original rabbit antisera.
It is important to conclude this in-depth discussion of the immune-mediated mechanisms of isolated and recurrent pregnancy loss by suggesting that pregnancy may not require an intact maternal immune system. Supporting this concept are data showing that agammaglobulinemic animals and women can successfully reproduce (282). Further, viable births also occur among women with severe immune deficiencies and in murine models that lack T and B cells (severe combined immunodeficiency [SCID] mice) and those that display a congenital absence of their thymus (nude mice). Still, immune factors may play important roles in a significant proportion of patients with recurrent pregnancy loss, and their presence is the subject of abundant research. Until this role is better defined, an understanding of contemporary immunologic hypotheses fosters the informed consideration of novel findings.
Male Factors
Most publications that review testing and treatment for recurrent pregnancy loss couples, including this chapter, recommend only a single test for the male partner in the couple—a peripheral blood karyotype. The role of the male partner in the etiology of recurrent pregnancy loss is understudied, but there is a growing body of literature suggesting that the development and validation of novel testing and treatment regimens for the male may prove beneficial (283,284). Detailed peripheral chromosomal testing of men whose partners experienced recurrent pregnancy loss revealed an increased incidence of Y chromosome microdeletions when compared to male partners in fertile and infertile couples (285). Small studies demonstrated that male partners in couples experiencing recurrent pregnancy loss have an increased incidence of sperm chromosomal aneuploidy, particularly sex chromosome disomy, when compared to fertile men (16,286). The addition of specialized testing to a standard semen analysis among men in couples with recurrent loss revealed reductions in sperm functional testing (hypo-osmotic swelling, acrosome status, nuclear chromatin decondensation) and increased DNA fragmentation and lipid peroxidation when compared to fertile men or historical controls (287–289). The latter results suggest that these men may have abnormal levels of reactive oxygen species in their semen or that their sperm cells are particularly sensitive to these compounds. To this point, paternal carriage of the MTHFR C677T mutation and hyperhomocysteinemia were associated with both DNA damage and recurrent pregnancy loss (290). A single, small, uncontrolled treatment study using antioxidants among male partners in recurrent pregnancy loss couples who had high levels of sperm DNA damage or semen lipid peroxidation suggested favorable treatment outcomes (288).
Other Factors
It is increasingly evident that the implantation of the blastocyst within the uterine decidua involves an exquisitely scripted crosstalk between embryo and mother. Alterations in this dialogue often result in improper implantation and placental development. For instance, recurrent pregnancy loss has been linked to a dysregulation in the expression patterns of vascular endothelial growth factors (VEGFs) on the developing placenta and their requisite receptors within the maternal decidua (291). Cellular and extracellular matrix adhesion properties may also be involved in this dialogue. The concept of uterine receptivity has been emboldened by the description of endometrial integrins and the timing of integrin switching during implantation (292). Others have reported decreased levels of endometrial mucin secretion and reductions in the endometrial release of soluble intercellular adhesion molecule I among women with histories of recurrent pregnancy loss (293,294). Programmed cell death (apoptosis) may also play an essential role in normal placental development. Alterations in two important apoptotic pathways—Fas-Fas ligand and bcl2—have both been linked to recurrent pregnancy loss and poor pregnancy outcome (121,295).
Environmental Factors
A variety of environmental factors have been linked to sporadic and recurrent early spontaneous pregnancy loss. These are difficult studies to perform, because, in humans, they all must be retrospective and all are confounded by alternative or additional environmental exposures. Nevertheless, the following factors have been linked to pregnancy loss: exposure to medications (e.g., antiprogestogens, antineoplastic agents, and inhalation anesthetics), exposure to ionizing radiation, prolonged exposure to organic solvents, and exposure to environmental toxins, especially bisphenol-A and heavy metals (296–299). The latter two exposures have been demonstrated to have both endocrine and immune effects that could lead to poor placentation and subsequent pregnancy loss (300,301). Associations between spontaneous pregnancy loss and exposures to video display terminals, microwave ovens, high-energy electric power lines, and high altitudes (e.g., flight attendants) are not substantiated (302,303). There is no compelling evidence that moderate exercise during pregnancy is associated with spontaneous abortion. In the absence of cervical anatomic abnormalities or incompetent cervix, coitus does not appear to increase the risk for spontaneous pregnancy loss (304,305). Exposure to three particular substances—alcohol, cigarettes, and caffeine—deserves specific attention. Although some conflicting data exist, one very large epidemiologic study has shown that alcohol consumption during the first trimester of pregnancy, at levels as low as three drinks per week, is associated with an increased incidence of spontaneous pregnancy loss (306–308). Cigarette smoking has also been linked to early spontaneous pregnancy loss; however, this is also not without controversy (309–311). Alcohol and tobacco intake in the male partner correlates with the incidence of domestic violence, which in turn is associated with early pregnancy loss (312). Finally, recent evidence adds to a growing body of literature that suggests consumption of coffee and other caffeinated beverages during early pregnancy is linked to adverse pregnancy outcome (309,313). The most publicized recent report casts doubt on the definition of a lower limit for safe use of caffeine in the first trimester of pregnancy (309). Obesity, stress at work, and use of nonsteroidal anti-inflammatory agents during early pregnancy have all been linked to an increased rate of isolated spontaneous pregnancy loss (314–317).
Preconception Evaluation
Investigative measures that are potentially useful in the evaluation of recurrent spontaneous abortion include obtaining a thorough history from both partners, performing a physical assessment of the woman (with attention to the pelvic examination), and a limited amount of laboratory testing (Table 33.3).
History
A description of all prior pregnancies and their sequence as well as whether histologic assessment and karyotype determinations were performed on previously aborted tissues are important aspects of the history. Approximately 60% of abortuses lost before 8 weeks of gestation were reported to be chromosomally abnormal; most of these pregnancies are affected by some type of trisomy, particularly trisomy 16 (318,319). The most common single chromosomal abnormality is monosomy X (45X), especially among anembryonic conceptuses (320). Aneuploid losses are particularly prevalent among women with recurrent pregnancy loss who are over the age of 35 (8). Although somewhat controversial, the detection of aneuploidy in miscarriage specimens may be less when the couple experiencing recurrent abortions is euploidic. Alternatively, some investigators have suggested that, because aneuploidy is common among miscarriage specimens from patients experiencing both isolated and recurrent spontaneous pregnancy losses, if aneuploidy is documented in fetal tissues from a recurrent pregnancy loss patient, this loss does not affect their prognosis for future pregnancy maintenance (13).
Most women with recurrent pregnancy losses tend to experience spontaneous abortion at approximately the same gestational age in sequential pregnancies (321). Unfortunately, the gestational age when pregnancy loss occurs, as determined by last menstrual period, may not be informative, because there is often a 2- to 3-week delay between fetal demise and signs of pregnancy expulsion (322). The designation of couples experiencing recurrent abortion into either primary or secondary categories is not helpful in either the diagnosis or management of most women with recurrent abortion. Approximately 10% to 15% of couples cannot be classified into either the primary or secondary category because, although their first pregnancy resulted in a loss, it was followed by a term delivery prior to subsequent losses.
Table 33.3 Investigative Measures Useful in the Evaluation of Recurrent Early Pregnancy Loss
It is important to glean any history of subfertility or infertility among couples with recurrent pregnancy loss. This is defined as the inability to conceive after 12 months of unprotected intercourse. By definition, 15% of all couples will meet this criteria; this number increases to 33% among couples with recurrent pregnancy losses. Because many pregnancies are lost before or near the time of missed menses, subfertility among recurrent pregnancy loss patients may in some cases reflect recurrent preclinical losses. Menstrual cycle history may provide information about the possibility of oligo-ovulation or other relevant endocrine abnormalities in recurrent pregnancy loss patients. An assessment of the timing of intercourse relative to ovulation should be reviewed with couples in an effort to detect dyssynchronous fertilization that could contribute to pregnancy loss (323). A personal and family history of thrombotic events or renal abnormalities may provide vital information. A family history of pregnancy losses and obstetric complications should be addressed specifically. Detailed information about drug and environmental exposure should also be obtained.
Physical Examination
A general physical examination should be performed to detect signs of metabolic illness, including PCOS, diabetes, hyperandrogenism, and thyroid or prolactin disorders. During the pelvic examination, signs of infection, DES exposure, and previous trauma should be ascertained. Estrogenization of mucosal tissues, cervical and vaginal anatomy, and the size and shape of the uterus should also be determined.
Laboratory Assessment
Valuable Tests
Laboratory assessment of couples with recurrent pregnancy losses should include the following:
1. Chromosome analysis of the products of conception
2. Parental peripheral blood karyotyping with banding techniques,
3. Assessment of the intrauterine cavity with either office hysteroscopy, sonohysterography, three-dimensional transvaginal sonography, or hysterosalpingography, followed by operative hysteroscopy if a potentially correctable anomaly is found (324),
4. Thyroid function testing, including serum thyroid-stimulating hormone levels,
5. Anticardiolipin, anti-β2 glycoprotein-1, and lupus anticoagulant testing (aPTT or Russell Viper Venom testing)
6. Platelet levels
Tests with Unproven Utility
A number of laboratory assessment tools are under investigation for use in patients with a history of recurrent pregnancy loss. At present, results are either too preliminary to warrant unfettered recommendation or studies of their use have been too contradictory to allow final determination of their value. Tests with unproven or unknown utility include:
1. Evaluation of ovarian reserve using day 3 serum follicle–stimulating hormone or antimüllerian hormone levels. It appears that decreased ovarian reserve may portend a poor outcome in all patients, including those with recurrent pregnancy loss (110,111).
2. Thrombophilia testing:
a. Factor V Leiden, G20210A prothrombin gene mutation, protein S activity
b. Serum homocysteine levels
c. If there is a family or personal history of venous thromboembolic events, obtain protein C activity and antithrombin activity.
d. Consider altering these screening paradigms based on ethnic background. Factor V Leiden and prothrombin promoter mutations are rare in African and Asian populations. Among Asian populations, protein C and protein S are the most common inherited thrombophilias.
3. Testing for serologic evidence of PCOS using luteinizing hormone or androgen values may be useful (89–92).
4. Testing for peripheral evidence of TH1/TH2 cytokine dysregulation. Although large studies failed to demonstrate association between peripheral cytokine alterations and pregnancy outcome among patients with recurrent pregnancy loss, smaller studies reported peripheral shifts toward TH1 profiles only in those recurrent pregnancy loss patients who subsequently lose their pregnancy (212,213). One study documented a shift toward TH1 profiles at the time of fetal demise in these patients; however, it is particularly difficult to determine cause and effect in this situation (325).
5. Preconceptional testing for the prevalence and activity of peripheral NK cells has been reported in small studies to reflect prognosis and to facilitate patient counseling (326,327). Still, peripheral NK cells may not adequately reflect those at the site of implantation, and this testing remains unproven.
6. Testing for antithyroid antibodies among women with recurrent pregnancy loss remains controversial, but is rapidly gaining support (98–100,103,271–273). Investigators have recently demonstrated an increased prevalence of these antibodies among women with a history of recurrent pregnancy loss, even in the absence of thyroid endocrinologic abnormalities (99,100,102,272).
7. Testing for the presence of a variety of autoantibodies (other than lupus anticoagulant and anticardiolipin antibody) has been hotly debated, but without consensus (245,246,249,262,328,329). Testing for some antiphospholipid antibodies, such as antiphosphatidylserine and anti-β2 glycoprotein-1, are particularly attractive because mechanistic connections between their presence and placental pathology were reported (246,260,261,263,264). Measurement of anti-β2 glycoprotein-1 antibodies was formally added to the criteria defining the antiphospholipid syndrome, and data are accumulating for specific relevance to pregnancy loss (245,246,251,330). Among patients with known autoimmune diseases and recurrent pregnancy loss additional antiphospholipid testing may also be warranted (331).
8. Cervical cultures for mycoplasma, ureaplasma, and chlamydia may be considered.
9. Interobserver reproducibility and accuracy are too low to reliably use the Noyes criteria to diagnose a luteal phase defect on timed endometrial biopsy (332). This tool lacks precision and does not alter clinical management (333). More specific and predictive methodology for diagnosing this disorder is not yet available.
The following investigations have no place in modern clinical care of patients with recurrent spontaneous pregnancy loss:
1. Evaluations that involve extensive testing for serum or site-specific auto- or alloantibodies (including antinuclear antibodies and antipaternal cytotoxic antibodies) are both expensive and unproven. Their use often verifies the statistical tenet that if the number of tests performed reaches a critical limit, the results of at least one will be positive in every patient.
2. Testing for parental HLA profiles is never indicated in outbred populations. Findings that HLA sharing is associated with poor pregnancy outcomes are strictly limited to those specific populations studied, which have very high and sustained levels of marriage within a limited community (279).
3. Use of mixed lymphocyte cultures has not proved useful. Use of other immunologic tests is unnecessary also unless these studies are performed, with informed consent, under a specific study protocol in which the costs of these experimental tests are not borne by the couple or their third-party payers.
4. Further work is necessary before suppressor cell or factor determinations, cytokine, oncogene, and growth factor measurements, or embryotoxic factor assessment can be clinically justified.
Postconception Evaluation
Following conception, close monitoring of patients with histories of recurrent pregnancy loss is advised to provide emotional support and to confirm intrauterine pregnancy and its viability. The incidence of ectopic pregnancy and complete molar gestation is increased in women with a history of recurrent spontaneous pregnancy loss. Although somewhat controversial, some data suggest that the risk of pregnancy complications other than spontaneous abortion are not significantly different between women with and without a history of recurrent losses (102,334–338). Two uncontested exceptions to this observation are those women who have antiphospholipid antibodies and those who have an intrauterine infection.
Determining serum levels of β-hCG may be helpful in monitoring early pregnancy until an ultrasonographic examination can be performed; however, not all investigators have found inadequate β-hCG levels in pregnancies that ultimately abort (339). Other hormonal determinations are rarely of benefit because levels are often normal until fetal death or abortion occurs (340).
The best method for monitoring in early pregnancy is ultrasonography. If used, serum β-hCG levels should be serially monitored from the time of a missed menstrual period until the level is approximately 1,200 to 1,500 mIU/mL, at which time an ultrasonographic scan is performed and blood sampling is discontinued. Ultrasonographic assessment may then be performed every 2 weeks until the gestational age at which previous pregnancies were aborted. The prognostic value of serial ultrasonography and a variety of hormonal and biochemical measurements during early pregnancy in women with histories of recurrent losses has been reported (341).
If a pregnancy has been confirmed, but fetal cardiac activity cannot be documented by approximately 6 to 7 weeks of gestation (by sure menstrual or ultrasonographic dating), intervention is recommended to expedite pregnancy termination and to obtain tissue for karyotype analysis. First trimester screening with maternal chemistries and fetal nuchal lucency measurement or chorionic villus sampling are recommended for obstetrical indications. Maternal serum can also be obtained for assessment at 16 to 18 weeks of gestation. Amniocentesis may be recommended to assess the fetal karyotype after the pregnancy has progressed past the time of prior losses.
The importance of obtaining karyotypic analysis from tissues obtained after pregnancy demise in a woman experiencing recurrent losses cannot be overemphasized. Results may suggest karyotypic anomalies in the parents. The documentation of aneuploidy may have important prognostic implications and may direct future interventions. Cost analysis has demonstrated that karyotypic analysis is financially prudent among patients with histories of recurrent pregnancy loss (342). Obtaining karyotypic data from aborted specimens incurs many difficulties in culturing cells from tissues that may have significant inflammation or necrosis and contamination of specimens with maternal cells. Efforts to develop methods that avoid such difficulties include the application of comparative genomic hybridization technology to recurrent pregnancy loss (343). This technology was used successfully on archived and paraffin-embedded pregnancy tissues (344). In the future, fetal karyotype assessment may also be performed using DNA isolated from nucleated fetal erythrocytes in maternal blood (345)
Therapy
Advances in the treatment of patients with recurrent pregnancy loss have been regrettably slow. Despite a rapid expansion in understanding the molecular and subcellular mechanisms involved in implantation and early pregnancy maintenance, extension of these concepts to prevention of recurrent early pregnancy loss has lagged. In addition to these limitations, progress toward treatment of most causes of recurrent pregnancy loss has been hampered by a variety of factors. The condition itself has been inconsistently defined. The results of clinical trials involving recurrent pregnancy loss patients therefore are nearly impossible to compare and evaluate. Trial design is frequently substandard, with lack of rationale, lack of appropriate controls, and poor statistical analysis, limiting the ability to draw rational conclusions from reported results. Finally, epidemiologic data indicate that most patients with a history of recurrent pregnancy loss will, in fact, have a successful pregnancy the next time they conceive (7). For these reasons, with few exceptions, most therapies for recurrent pregnancy loss must be considered experimental. Until further study is completed, treatment protocols involving these therapies should be undertaken only with informed consent and in the setting of a well-designed, double-blind, placebo-controlled clinical trial.
Common therapeutic options available for patients with recurrent pregnancy loss include the use of donor oocytes or sperm, the use of preimplantation genetic diagnosis, the use of antithrombotic interventions, the repair of anatomic anomalies, the correction of any endocrine abnormalities, the treatment of infections, and a variety of immunologic interventions and drug treatments. Psychologic counseling and support should be recommended for all patients.
Genetic Abnormalities
Recent evidence suggests that, in women with a history of three or more spontaneous pregnancy losses, a subsequent pregnancy loss has a 58% chance of chromosomal abnormality (15). Among women with recurrent pregnancy loss who are age 35 or older, the aneuploidy rate is much higher (8). The majority of chromosomal abnormalities identified in miscarriages are autosomal trisomies and considered to result from maternal nondisjunction. Maternal age appears as a consistent and important risk factor for trisomy in the majority of studies. There are several options for patients who suffer from recurrent pregnancy loss who have an identified miscarriage due to trisomy. The first is to conceive again without any specific change in medical management, as these abnormalities are sporadic and unlikely to recur. Studies examining patients with recurrent pregnancy loss show that women who miscarry chromosomally abnormal conceptions are more likely to achieve a live birth with subsequent pregnancy than those who miscarry chromosomally normal conceptions (13,346). A second involves preimplantation genetic diagnosis (PGD) or preimplantation screening, and a third involves the use of donor gametes.
Because chromosomal abnormalities are the most commonly identified cause of miscarriage, some have argued that the use of PGD is indicated for patients with recurrent pregnancy loss. PGD involves the removal of a single cell from an in vitro–matured embryo. Genetic testing can be performed on this cell to examine chromosomal composition for the presence of single gene disorders (e.g., cystic fibrosis) or abnormalities in chromosome number and morphology. Embryos that are diagnosed with genetic abnormalities would be discarded and only those embryos with normal results would be considered appropriate for transfer into the uterus. Use of PGD in patients with known heritable genetic disorders (e.g., cystic fibrosis, X-linked disorders) is presently in widespread use in internationally recognized assisted reproductive technology centers.
The use of PGD has the potential to reduce the incidence of pregnancy loss arising from a genetic etiology. However, definitive studies in this population have not yet been done. The use of PGD requires the patient to go through an IVF cycle to obtain embryos for biopsy, and the impact of the biopsy technique itself on the embryos' viability is not known at this time. Although there are several retrospective studies showing reduced miscarriage rates with this technique, several prospective trials using the outcome of successful pregnancy per started cycle fail to show any benefit (347–357). IVF is invasive and costly and many patients with recurrent pregnancy loss conceive quickly without intervention and have a high likelihood of live birth with their subsequent pregnancy. Therefore, the optimal control group for a study of IVF PGD in the recurrent pregnancy loss population is debated. Should it be natural conceptions or IVF without PGD? Finally, the prognosis for a patient with recurrent pregnancy loss does seem to be linked to the chromosome analysis of prior miscarriages. Recurrent pregnancy loss patients who miscarry chromosomally abnormal embryos, seem to have better prognosis than those who miscarry chromosomally normal conceptions, again arguing for expectant management for recurrent pregnancy loss patients with a history of aneuploid loss. On the other hand, patients with poorer prognosis are those who miscarry chromosomally normal embryos and therefore would not benefit from PGD. The efficacy of PGD in the treatment of patients with recurrent pregnancy loss continues to be investigated, and the method of embryo biopsy and genetic testing continues to evolve (355,356). As these techniques improve and the understanding of aneuploidy and recurrence improves, there may be a subset of recurrent pregnancy loss patients, such as carriers of parental translocations, who might benefit from this intervention. At this time it cannot be recommended for all patients with a history of recurrent pregnancy loss.
The third approach is to use donor eggs or sperm. This treatment is particularly useful for patients with parental genetic factors and recurrent pregnancy loss, for example, a patient with Robertsonian translocations involving homologous chromosomes. In these patients, their genetic anomaly always results in unbalanced gametes, and the use of donor oocyte or donor sperm is recommended. Use of donor gametes among patients with a history of recurrent pregnancy loss can be useful in other cases where couples are at higher risk for unbalanced offspring because of carrying other forms of chromosomal rearrangements, such as reciprocal translocations or advanced maternal age. In these cases use of donor gametes was demonstrated to be as effective as its use in matched patients without such a history (358). In all cases of balanced translocations or embryonic aneuploidy, genetic counseling is recommended.
Anatomic Anomalies
Hysteroscopic resection represents state-of-the-art therapy for submucous leiomyomas, intrauterine adhesions, and intrauterine septa. This approach appears to limit postoperative sequelae while maintaining efficacy in terms of reproductive outcome (72,76,77,358–362). Use may be safely extended to patients with DES exposure, hypoplastic uteri, and complicated septal anomalies(76,77,363). Attempts to improve on standard hysteroscopic metroplasty, which is typically performed in the operating room using general anesthesia, often with laparoscopic guidance, are under investigation. Ultrasonographically guided transcervical metroplasty is reported to be safe and effective (359). Ambulatory, office-based procedures, including septum resection under fluoroscopic guidance, are attractive options (360).
For patients with a history of loss secondary to cervical incompetence, placement of a cervical cerclage is indicated. This is usually performed early in the second trimester after documentation of fetal viability. Cervical cerclage should be considered as a primary intervention for women with DES-associated uterine anomalies.
Endocrine Abnormalities
Some investigators have proposed the use of ovulation induction for the treatment of recurrent pregnancy loss (361,362). The theory behind its use in these patients rests on hypotheses that ovulation induction is associated with healthier oocytes. Healthier oocytes, in turn, may decrease the incidence of luteal phase insufficiency, which should result in improved pregnancy maintenance. This approach grossly oversimplifies the mechanisms involved in implantation and early pregnancy maintenance. Until appropriately studied, use of empiric ovulation induction for treatment of unexplained recurrent pregnancy loss should be viewed with caution. Evidence from small studies indicates such use is not effective (361). Still, use of ovulation induction in some subsets of patients with recurrent pregnancy loss could be of benefit. For instance, stimulating folliculogenesis with ovulation induction or luteal phase support with progesterone should be considered for women with luteal phase insufficiency. The efficacy of these therapies, however, is not substantiated (363). Ovulation induction might also be beneficial for women with hyperandrogen and LH hypersecretion disorders, especially following pituitary desensitization with gonadotropin-releasing hormone agonist therapy (112). This treatment remains controversial because the only large, prospective, randomized controlled trial to date reports no therapeutic efficacy; none for prepregnancy pituitary suppression nor for luteal phase progesterone supplementation (364).
Links between PCOS, hyperandrogenism, hyperinsulinemia, and recurrent pregnancy loss make use of insulin-sensitizing agents in the treatment of recurrent pregnancy loss associated with PCOS attractive (89–92). Although further study is needed, there are an increasing number of reports that support its use for this application (365,366). Prepregnancy glycemic control may be particularly important for women with overt diabetes mellitus (93,95). Thyroid hormone replacement with Synthroid may be helpful in cases of hypothyroidism. There are data indicating that thyroid hormone therapy may be of some benefit in euthyroid recurrent loss patients with antithyroid antibodies and possibly even in all pregnant women with “euthyroid” TSH levels between 2.5 and 5.0 mIU/L (98–100,272). There does not appear to be a place in the medical management of recurrent pregnancy loss for adding bromocriptine in women who do not have a prolactin disorder.
Infections
Empiric antibiotic treatment has been used for couples with recurrent abortion. Its efficacy is unproven. Elaborate testing for infectious factors among recurrent pregnancy loss patients and use of therapeutic interventions is not justified unless a patient is immunocompromised or a specific infection has been documented (113). For cases in which an infectious organism has been identified, appropriate antibiotics should be administered to both partners, followed by posttreatment culture to verify eradication of the infectious agent before attempting conception.
Immunologic Factors
Immune-mediated recurrent pregnancy loss has received more attention than any other single etiologic classification of recurrent pregnancy loss. Nevertheless, the diagnosis and subsequent treatment of the majority of cases remains unclear (102,367–370). Most therapies for proposed immune-related recurrent pregnancy loss must be considered experimental. As stated earlier, it is known that the developing conceptus contains paternally inherited gene products and tissue-specific differentiation antigens, and that there is maternal recognition of these antigens (216–218). Historically, it has been speculated that either inappropriately weak immune responses to these antigens or unusually strong responses could result in early pregnancy loss. As a consequence, both immunostimulating and immunosuppressive therapies have been proposed, but no conclusions about efficacy can be drawn.
Immunostimulating Therapies: Leukocyte Immunization
Stimulation of the maternal immune system using alloantigens on either paternal or pooled donor leukocytes has been promoted for patients with immunologic recurrent pregnancy loss, and a number of reports support possible mechanisms for potential therapeutic value (371–375). Both individual clinical trials and meta-analyses, however, continue to report conflicting results concerning the efficacy of leukocyte alloimmunization in patients with recurrent pregnancy loss (25,364,365,372,376–379). This most certainly reflects the remarkable heterogeneity in study design, patient selection, and therapeutic protocols, as well as the typically small numbers of enrolled subjects in these investigations. One of the largest trials evaluating the efficacy of leukocyte immunization in patients with unexplained recurrent pregnancy loss is a part of the Recurrent Miscarriage (REMIS) study (380). This investigation was large (over 90 patients per treatment arm), prospective, placebo controlled, randomized, and double blinded. It demonstrated no efficacy for paternal leukocyte immunization in couples with unexplained recurrent pregnancy loss. The most recent and best of the meta-analyses definitively rejects use of this therapy in patients with recurrent loss (381). Leukocyte immunization also poses a significant risk to both the mother and her fetus (344,345,382). Several cases of graft-versus-host disease, severe intrauterine growth retardation, and autoimmune and isoimmune complications have been reported (25,378,382–386). In addition, alloimmunization to platelets contained in the paternal leukocyte preparation is associated with cases of potentially fatal fetal thrombocytopenia. The routine use of this therapy for recurrent abortion cannot be clinically justified at this time. The procedure should be performed only as part of an appropriately controlled trial using informed consent. All costs associated with this treatment should be borne by the investigators until its efficacy has been demonstrated.
Other immunostimulating therapies have been proposed and abandoned. Intravenous preparations consisting of syncytiotrophoblast microvillus plasma membrane vesicles have been used to mimic the fetal cell contact with maternal blood that normally occurs in pregnancy (387). The efficacy of this therapy has not been established (381,387,388). The use of third-party seminal plasma suppositories has also been attempted, based on the misconception that TLX was part of an idiotype–anti-idiotype control system (389,390). Third-party seminal plasma suppositories for recurrent abortion have no scientifically credible rationale and should not be used.
Immunosuppressive Therapies
Immunosuppressive and other immunoregulating therapies have been advocated for cases in which abortion was believed to result from antiphospholipid antibodies or inappropriate cellular immunity toward the implanting fetus. Again, study design problems, including small numbers of recruited patients, lack of prestratification by maternal age and number of prior losses before randomization, and other methodologic and statistical inaccuracies preclude definitive statements regarding therapeutic efficacy for most of the proposed immunosuppressive approaches.
Intravenous Immunoglobulin
Intravenous immunoglobulins (IVIgs) are composed of pooled samples of immunoglobulins harvested from a large number of blood donors. Studies on the use of IVIg therapy in the treatment of recurrent pregnancy loss are based on the theory that some recurrent pregnancy loss patients have an overzealous immune reactivity to their implanting fetus. IVIgs do have immunosuppressive effects, but the mechanisms underlying this immune modulation are only partially understood. These mechanisms may include decreased autoantibody production and increased autoantibody clearance, T-cell and Fc-receptor regulation, complement inactivation, enhanced T-cell suppressor function, decreased T-cell adhesion to the extracellular matrix, and downregulation of TH1 cytokine synthesis (391–394). Based on a large number of relatively small studies using a variety of treatment protocols, there remains no conclusive evidence to suggest that use of IVIg in the treatment of patients with unexplained (and presumed immunologic) recurrent pregnancy loss has any benefit (383,395–399). This includes a recent trial using IVIg in women with secondary recurrent pregnancy loss that was ended early because interim analyses revealed no effect (395). The Cochrane review of immune therapy for recurrent pregnancy loss also addressed IVIg therapy and reported that its use did not alter pregnancy outcomes in patients with otherwise unexplained recurrent pregnancy loss (381,388). Improved posttreatment pregnancy rates may be seen, however, when IVIg is used in those specific patients with autoimmune-mediated pregnancy loss associated with APS (400,401). Therapy with IVIgs for recurrent pregnancy loss is expensive, invasive, and time-consuming, requiring multiple intravenous infusions over the course of pregnancy (402). Side effects of IVIg therapy include nausea, headache, myalgias, and hypotension. More serious adverse effects include anaphylaxis (particularly in patients with IgA deficiency) (403).
Progesterone
As mentioned earlier, progesterone also has known immunosuppressive effects (220–223,227,228). A number of studies using in vitro cellular systems relevant to the maternal–fetal interface have now demonstrated that progesterone either inhibits TH1 immunity or causes a shift from TH1- to TH2-type responses (208,227,228,404). Although the mechanism of action remains unclear, a recent Cochrane review concluded that progesterone supplementation was effective in the treatment of recurrent, but not isolated, spontaneous pregnancy loss (405,406). The review makes no recommendations on dosage, timing of initiation, nor route of progesterone administration. Progesterone has been administered both intramuscularly and intravaginally for the treatment of recurrent pregnancy loss. It is thought that vaginal administration may increase local, intrauterine concentrations of progesterone better than systemic administration. Vaginal formulations may therefore provide a better method of attaining local immunosuppressive levels of progesterone while averting any adverse systemic side effects.
Intralipid Infusion
The relative paucity of inflammatory diseases among the Greenland Inuit population, who consume a diet high in fish oils, led investigators to study the immune modulatory effects of lipid emulsions in total parenteral nutrition preparations for preoperative patients and for burn and trauma victims (406–409). The wide range of demonstrated effects, including lipid preparations that reduced natural killer cell activity, reduced monocytes proinflammatory cytokine production and increased susceptibility to infection, led investigators to hypothesize, as early as 1994, that lipid infusions might promote an immune environment that would favor pregnancy maintenance (410). Since that time, a small number of publications have addressed the effects of lipid infusions (Intralipid) in women with a history of pregnancy loss (411,412). These investigations have demonstrated a decrease in peripheral natural killer cell activity in women treated with one to three infusions of Intralipid. This effect lasted from 4 to 9 weeks after the last infusion (411). The authors did not address NK cell cytokine secretion patterns nor did they assay decidual NK cell function. Despite this paucity of data, Intralipid infusions are being administered to recurrent pregnancy loss patients with increasing frequency. The existing data do not support this practice. At this time, Intralipidinfusions in recurrent pregnancy loss patients should only be administered under an institutional review board–approved protocol and in a study setting. They should not generate clinical income.
TNF-α Inhibition
Interest in the potent proinflammatory cytokine, TNF-α, as a mediator of pregnancy loss came out of the description of the TH1 and TH2 paradigm (209). Over the past 10 years, there have been several publications that link maternal serum TNF-α levels and activating TNF-α gene promoter polymorphisms to recurrent pregnancy loss (413–415). The development of antagonists of TNF-α in the form of blocking antibodies (adalimumab, infliximab) and inhibitory recombinant proteins (etanercept) has allowed for successful treatment of several autoimmune disorders, including rheumatoid arthritis, psoriasis, and Crohn’s disease. Their use, however, has not been associated with universally positive outcomes and may worsen some disorders, including multiple sclerosis (416). These products are associated with rare but worrisome side effects, including liver failure, aplastic anemia, interstitial lung disease, and anaphylaxis (417). Although there exists only a single, small, retrospective, observational, nonrandomly assigned case series that involved treatment of recurrent pregnancy loss patients with inhibitors of TNF-α, these positive preliminary results have led a growing number of clinics to offer this therapy to patients, often at a significant cost (418). The safety of these compounds in pregnancy has not been appropriately studied, and preliminary reports associating exposure to TNF-α inhibitors during early pregnancy to fetal VACTERL syndrome is concerning (419). As with Intralipid therapy, use of TNF-α inhibition for the treatment of recurrent pregnancy loss should only be administered under an institutional review board–approved protocol in a study setting and should not generate clinical income.
Other immunoregulating therapies theoretically useful in treating recurrent pregnancy loss include the use of cyclosporine, pentoxifylline, and nifedipine, although maternal and fetal risks with these agents preclude their clinical use. Plasmaphoresis has also been used to treat women with recurrent abortion and antiphospholipid antibodies (420). Generalized immunosuppression with corticosteroids, such as prednisone, has been advocated during pregnancy for women with recurrent losses and chronic intervillositis and those with recurrent pregnancy loss and APS (421). Although corticosteroids have shown some treatment promise in these patients, maternal and fetal side effects and the availability of alternative therapies have limited their use (421,422). That said, in response to successful use of prednisolone in a woman with 10 prior losses, Quenby et al. have demonstrated that such treatment decreases the number of uterine NK cells in the peri-implantation decidua among women with a history of recurrent loss and have plans for a trial of therapy using live birth as a secondary outcome (423–425). The efficacy and side effects of prednisoneplus low-dose aspirin was examined in a recent, large, randomized, placebo-controlled trial treating patients with autoantibodies and recurrent pregnancy losses. Pregnancy outcomes for treated and control patients were similar; however, the incidence of maternal diabetes and hypertension and the risk of premature delivery were all increased among those treated with prednisone and aspirin (426).
Antithrombotic Therapy
Therapy for patients with recurrent pregnancy losses associated with either APS or other thrombophilic disorders has now shifted toward the use of antithrombotic medications. Unlike immunosuppressive treatments, this approach appears to address the effect (hypercoagulability), but not the underlying cause (e.g., genetic, APS) of recurrent pregnancy loss. However, there are reports that heparin, one typical anticoagulant, may exert direct immunomodulatory effects by binding to antiphospholipid antibodies and may decrease movement of inflammatory cells to sites of alloantigen exposure (427,428). The combined use of low-dose aspirin (75 to 80 mg per day) and subcutaneous unfractionated heparin (5,000 to 10,000 units twice daily) during pregnancy has been best studied among women with APS and appears to be efficacious (429–433). A typical regimen for women with antiphospholipid antibody syndrome would include use of aspirin (80 mg every day) beginning with any attempts to conceive. After pregnancy has been confirmed, 10,000 IU unfractionated sodium heparin is administered subcutaneously twice daily, throughout gestation. An aPTT should be obtained weekly and dosages of heparin should be adjusted until anticoagulation is achieved. Patients using this therapy should be treated in conjunction with a perinatologist because of their increased risks for preterm labor, premature rupture of the membranes, intrauterine growth restriction, intrauterine fetal demise, and pre-eclampsia. Other potential risks include gastric bleeding, osteopenia, and abruptio placenta.
Attempts have recently been made to extend the finding that antithrombotic therapy is efficacious when used to treat patients with APS and recurrent pregnancy loss in a number of directions. These directions include the use of low-molecular weight heparins (LMWH), the use of antithrombotic therapy in non-APS patients with thrombophilia and recurrent pregnancy loss, and even its use among recurrent pregnancy loss patients without thrombophilia (unexplained recurrent losses).
New formulations of heparin, termed low-molecular weight heparins, have been demonstrated to be superior to unfractionated heparin in the treatment of many clotting disorders (434–436). LMWH has the advantage of an increased antithrombotic ratio when compared with unfractionated heparin. This results in improved treatment of inappropriate clotting but fewer bleeding side effects. In addition, LMWH has been associated with a decreased incidence of thrombocytopenia and osteoporosis when compared with its unfractionated counterpart. Finally, LMWH has a long half-life and requires less frequent dosing and monitoring, thereby improving patient compliance. LMWH appear to be safe for use in pregnancy, and LMWH has shown promise when combined with low-dose aspirin in the treatment of recurrent pregnancy loss associated with APS (430,435,437). Only a few studies have compared the use of unfractionated heparin and aspirin to LMWH and aspirin in the treatment of women with APS and adverse pregnancy outcomes (433,438). The therapies had similar effects in one study (438). A meta-analysis suggested that unfractionated heparin was superior to LMWH, however, there was significant heterogenicity between studies (433). Efficacy has been suggested for LMWH treatment for patients with recurrent pregnancy loss associated with other thrombophilias, including activated protein C resistance associated with factor V Leiden, mutations in the promoter region of the prothrombin gene, and decreases in protein C and protein S activities (63,439–441). The use of LMWH for this indication appears to have an excellent safety profile for mother and fetus (437,442,443).
The prophylactic use of daily-low dose aspirin has become common practice within the lay public based on its perceived cardiovascular effects combined with its low incidence of side effects. Its sole use in the treatment of recurrent pregnancy loss has likewise gained momentum, and many patients with histories of recurrent loss will either be self-prescribing this therapy or will inquire about its usefulness. At present, there are no good data supporting its use either in patients with heritable thrombophilias or in the general recurrent pregnancy loss population. Although studies are small, the use of low-dose aspirinalone has not been shown to be effective in the treatment of recurrent pregnancy loss associated with APS (431,444,445). When used in these patients, it should be in combination with unfractionated or LMWH. Large randomized prospective trials examining the empiric use of aspirin alone or in combination with prophylactic doses of heparin have shown no benefit of these therapies in unexplained recurrent pregnancy loss (445). In addition, the use of aspirin in early pregnancy has been called into question with reports of an increased incidence of isolated spontaneous pregnancy loss among women who used this medication (316,317). However, these reports are poorly designed and do not adequately address the level of aspirin exposure (81 mg vs. 325 mg). Although reviews have touted the overall safety of aspirinin pregnancy, outside of use in combination with heparin for patients with recurrent pregnancy loss and APS, this medication should be used only with justification in the well-informed patient during early pregnancy (446).
More directed antithrombotic therapies have also been described for the treatment of recurrent pregnancy loss among patients with thrombophilias. For instance, the use of protein C concentrates has been reported to be associated with favorable pregnancy outcome in a patient with a history of thrombosis, recurrent fetal losses, and protein C deficiency (447).
As mentioned previously, vitamins B6, B12, and folate are important in homocysteine metabolism, and hyperhomocysteinemia is linked to recurrent pregnancy loss (21,23,38,66,68,72). Women with recurrent pregnancy loss and isolated fasting hyperhomocysteinemia should be offered supplemental folic acid (0.4 to 1.0 mg per day), vitamin B6 (6 mg per day), and possibly vitamin B12 (0.025 mg per day) (448–451). Fasting homocysteine levels should be retested after treatment. If levels are normalized or remain only marginally elevated, no further therapy is necessary. Homocysteine levels will predictably decrease during pregnancy.
Treatment of women with recurrent pregnancy loss and an identified inherited or acquired thrombophilia should be based on accompanying history. Currently, there are no prospective controlled trials examining the benefit of anticoagulation for the prevention of miscarriage in the absence of APS, and, therefore, anticoagulation recommendations for patients with inherited thrombophilias are based on individualized risk of venous thromboembolic events in pregnancy (28).
• If a venous thromboembolic event occurs during the index pregnancy, posthospitalization management requires therapeutic anticoagulation.
UFH: 10,000 to 15,000 U subcutaneous every 8 to 12 hours (monitor to keep aPTT 1.5 to 2.5 times normal) OR
LMWH: enoxaparin 40 to 80 mg subcutaneous twice a day or dalteparin 5,000 to 10,000 U subcutaneous twice a day). Consider monitoring trough factor Xa levels in the third trimester.
• If there is a personal history of venous thromboembolic events (particularly in a previous pregnancy or with hormonal contraceptive use) or a strong thrombophilic family history, treat with therapeutic anticoagulation. Thrombotic risk is greatest during the postpartum period.
• Anticoagulation should be reinitiated after delivery in doses reflecting predelivery treatment regimens. Postpartum anticoagulation should be continued for 6 to 12 weeks postpartum (435). Women may continue injectable therapy or transition to oral anticoagulants (e.g., coumarin). Use of heparin or of coumarin derivatives does not prohibit breastfeeding.
Psychological Support
There is no doubt that experiencing both isolated and recurrent losses can be emotionally devastating. The risk of major depression is increased greater than twofold among women with spontaneous pregnancy loss; in most women it arises in the first weeks following delivery (452). A caring and empathetic attitude is prerequisite to all healing. The acknowledgment of the pain and suffering couples have experienced as a result of recurrent abortion can be a cathartic catalyst enabling them to incorporate their experience of loss into their lives rather than their lives into their experience of loss (112). Referrals to support groups and counselors should be offered. Self-help measures, such as meditation, yoga, exercise, and biofeedback may also be useful.
Prognosis
The prognosis for successful pregnancy depends both on the potential underlying cause of pregnancy loss and (epidemiologically) on the number of prior losses (Table 33.4). As previously discussed, epidemiologic surveys indicate that the chance of a viable birth even after four prior losses may be as high as 60%. Depending on the study, the prognosis for successful pregnancy in couples with a cytogenetic etiology for reproductive loss varies from 20% to 80% (453–455). Women with corrected anatomical anomalies may expect a successful pregnancy in 60% to 90% of cases (74,453,456–459). A success rate higher than 90% has been reported for women with corrected endocrinologic abnormalities (454). Between 70% to 90% of pregnancies reported among women receiving therapy for antiphospholipid antibodies have been viable (460,461).
Table 33.4 Prognosis for a Viable Birth
|
Following: |
|
|
One spontaneous loss |
76% |
|
Two spontaneous losses |
70% |
|
Three spontaneous losses |
65% |
|
Four spontaneous losses |
60% |
|
With: |
|
|
Genetic factors |
20%–80% |
|
Anatomic factors |
60%–90% |
|
Endocrine factors |
>90% |
|
Infectious factors |
70%–90% |
|
Antiphospholipid antibodies |
70%–90% |
|
TH1 cellular immunity |
70%–87% |
|
Unknown factors |
40%–90% |
|
Following detection of fetal cardiac activity: |
|
|
Unexplained recurrent pregnancy loss |
77%–97% |
|
Antiphospholipid antibody syndrome and recurrent pregnancy loss |
Much lower |
Many forms of pre- or postconceptional tests have been proposed to help predict pregnancy outcome (201,219,327,462,463); none have been fully substantiated in large, prospective trials. The documentation of fetal cardiac activity on ultrasound may offer prognostic value; however, it appears that its predictions may be greatly affected by any underlying diagnosis. In one study, the live birth rate following documentation of fetal cardiac activity between 5 to 6 weeks from the last menstrual period was approximately 77% in women with two or more unexplained spontaneous abortions (464). It may be important to note that the majority of the patients in this study had evidence of inappropriate antitrophoblast cellular immunity. Others have shown that 86% of patients with antiphospholipid antibodies and recurrent pregnancy loss had fetal cardiac activity detected prior to subsequent demise (465). A prospective, longitudinal, observational study of 325 patients with unexplained recurrent pregnancy losses demonstrated that only 3% of 55 miscarriages occurred following the detection of fetal cardiac activity using transvaginal ultrasonography (466).
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