A diagnosis of chronic hypertension complicating pregnancy is made whenever hypertension precedes pregnancy or occurs prior to 20 weeks’ gestation. Shown in Table 47-1 are blood pressure thresholds for diagnosis of hypertension in adults. In most women with chronic hypertension, increased blood pressure is the only finding. Some women have preexisting complications that put the pregnancy at risk, including hypertensive or ischemic cardiac disease, renal insufficiency, or prior stroke. Predisposing factors for chronic hypertension include obesity and heredity. Women with chronic hypertension are at considerably increased risk for superimposed preeclampsia, which, in turn, substantially increases risks for preterm delivery and other pregnancy complications such as abruptio placentae and fetal growth restriction.
TABLE 47-1. Classification and Management of Blood Pressure for Adults
EFFECTS OF CHRONIC HYPERTENSION ON PREGNANCY
Most women taking antihypertensive medication whose hypertension is well controlled prior to pregnancy do well, although they remain at some risk for placental abruption and superimposed preeclampsia. The risk of maternal mortality increases from 10 in 100,000 to 230 in 100,000 live births in women with chronic hypertension.
The incidence of abruption increases from 1 in 200 to 300 in nonhypertensive women to 1 in 50 in women with mild chronic hypertension and 1 in 12 in women with severe hypertension. Smoking further increases this risk.
It is generally accepted that women with chronic hypertension are at increased risk for superimposed preeclampsia, and that this complication supervenes in at least 25 percent of women.
Forced preterm delivery due to severe superimposed preeclampsia and fetal growth restriction due to hypertensive vascular disease involving the placenta are the major causes of perinatal mortality and morbidity in women with chronic hypertension (see Table 47-2).
TABLE 47-2. Selected Pregnancy Outcomes in Women with Chronic Hypertension, Superimposed Preeclampsia, or Who Required Antihypertensive Treatment Early in Pregnancy
The incidence of fetal growth restriction occurs in direct relation to the severity of maternal hypertension. Advanced maternal age; the severity of hypertension and need for additional antihypertensive medication; and the presence of end-organ damage, such as renal or cardiac dysfunction, add to the risk of fetal growth restriction. The effect of antihypertensive therapy in women with mild chronic hypertension predating pregnancy is unclear. Although such treatment is not harmful for the mother, the potential benefits or adverse fetal-neonatal effects have not been determined.
PRECONCEPTIONAL AND EARLY PREGNANCY EVALUATION
Ideally women with chronic hypertension should be counseled and evaluated prior to pregnancy. The duration of chronic hypertension, level of blood pressure control and antihypertensive therapy is ascertained. General health, daily activities, diet, and adverse personal behaviors should be determined. Adverse events such as cerebrovascular accident, myocardial infarction, cardiac failure, or renal dysfunction are especially pertinent.
Evaluation also includes assessment of renal, hepatic, and cardiac function. Cardiac assessment should be targeted toward ascertainment of any dysrhythmias or evidence of left ventricular hypertrophy, indicating either longstanding or poorly controlled hypertension, or both. Women with appreciable left-ventricular hypertrophy are at increased risk for cardiac dysfunction and congestive heart failure during pregnancy. In women with any prior adverse outcome, or in long-term hypertension, echocardiography is indicated.
Renal function is assessed by serum creatinine and quantification of protein-uria. If either is abnormal, these women are at further increased risk for adverse effects on pregnancy. It can be difficult, however, to separate the effects of the pregnancy from inevitable progression of renal disease. As a general principle, although not precisely linear, renal insufficiency is inversely proportional to increased risk of hypertensive complications on pregnancy outcomes. Pregnancy is relatively contraindicated in women who, despite therapy, maintain persistent diastolic pressures of 110 mm Hg or greater, require multiple antihypertensives, or whose serum creatinine is greater than 2 mg/dL. Stronger contraindications include women who have had prior cerebrovascular thrombosis or hemorrhage, myocardial infarction, or cardiac failure.
MANAGEMENT DURING PREGNANCY
The goal in women whose pregnancy is complicated by chronic hypertension is to minimize or prevent any of the adverse maternal or perinatal outcomes previously discussed. In general, management is targeted toward prevention of moderate or severe hypertension as well as prevention of severe superimposed preeclampsia. Recommended behavioral modification includes dietary counseling and reduction of smoking, alcohol, cocaine, or other substance abuse. It is accepted that women with severe hypertension must always be treated for maternal indications regardless of pregnancy status. This includes pregnant women with prior adverse outcomes, including cerebrovascular events, myocar-dial infarction, and cardiac or renal dysfunction. We agree with the philosophy of beginning antihypertensive treatment in an otherwise healthy woman with persistent diastolic pressures of 100 mm Hg or greater.
Antihypertensive Treatment during Pregnancy
Continued antihypertensive treatment for pregnant women with chronic hypertension already taking such medications at the onset of pregnancy is debated. Although beneficial to the mother to reduce her blood pressure, the lower pressure could theoretically decrease uteroplacental perfusion and jeopardize the fetus. Studies of chronic hypertension treatment in pregnancy have not shown a decreased incidence in the development of superimposed preeclampsia. One important observation of recent studies has been that no adverse outcomes were found in the treatment group. Thus, it is not unreasonable to treat women with uncomplicated mild or moderate sustained chronic hypertension who would otherwise be prescribed antihypertensive therapy when they were not pregnant. The theoretical concern of fetal growth restriction due to reduced placental perfusion by lowering maternal blood pressure is confounded in that worsening blood pressure itself is associated with abnormal fetal growth.
Antihypertensive Drug Selection
Several different categories of antihypertensive drugs have been used in pregnant women. Good results have been obtained with α-methyldopa, and its use in pregnancy has been considered safe. Adrenergic drugs, especially labetalol, have also been used, especially in Europe, but an advantage over α-methyldopa has not been shown. Atenolol, however, has been associated with growth restriction and should be avoided in pregnancy. Nifedipine use has been reported, but the data are too limited to make recommendations for routine use in pregnancy. Largely for theoretical concerns, diuretics are usually not instituted as first-line therapy during pregnancy, particularly after 20 weeks. The fear is that diuretics would decrease circulating blood volume and predispose to placental insufficiency. Angiotensin-converting enzyme inhibitors are associated with fetal malformations and are not used during pregnancy.
Women with well-controlled chronic hypertension and no prior complicating factors can generally be expected to have a good pregnancy outcome. Because even otherwise healthy women with mild hypertension have an increased risk of abruptio placentae, superimposed preeclampsia, preterm delivery, and fetal growth restriction, serial antepartum assessment of fetal well-being is usually recommended (see Chapter 12). The gestational age at which to initiate such testing varies with the severity of the disease and the overall clinical course.
Diagnosis of Superimposed Preeclampsia
The diagnosis of superimposed preeclampsia may be difficult to make in women with chronic hypertension. Criteria that support the diagnosis of superimposed preeclampsia include the development of proteinuria; worsening of preexisting proteinuria; neurological symptoms, including severe headaches and visual disturbances; oliguria; and convulsions or pulmonary edema. Laboratory abnormalities that support the diagnosis include increasing serum creatinine level, thrombocytopenia (<100,000 platelets per mm3), or appreciable elevation of serum hepatic transaminase levels.
In women with uncomplicated, well-controlled chronic hypertension and an otherwise normal pregnancy course, and with normal fetal growth and amnionic fluid volume, it is the practice at our institution to await labor at term. In women with complications or those in whom fetal testing becomes abnormal, induction of labor is considered. In general, vaginal delivery is attempted. This includes women with severe preterm superimposed preeclampsia.
Many women with chronic hypertension and superimposed severe preeclampsia have contracted blood volumes compared with normal pregnant women. These women have marked vasoconstriction and, in general, have increased blood loss, which may cause oliguria postpartum. It may be difficult and hazardous to attempt to maintain intravascular volume and renal perfusion solely with intravenous crystalloid or colloid solutions in these women. Blood transfusion may be necessary to maintain intravascular volume to ensure tissue perfusion. Left-ventricular workload may be increased in these women when interstitial fluid is mobilized for excretion during the immediate postpartum period. Cerebral edema, heart failure, pulmonary edema, and renal dysfunction are complications that can be seen in this setting.
For further reading in Williams Obstetrics, 21st ed.,
see Chapter 45, “Chronic Hypertension.”