First-Trimester Ultrasound: A Comprehensive Guide

19. Fetal Anomalies

Ana Monteagudo Margaret Dziadosz2, 3   and Ilan E. Timor-Tritsch 

(1)

Department of Obstetrics and Gynecology, NYU School of Medicine, 550 First Avenue, NBV-9N1, New York, NY 10016, USA

(2)

Department of Obstetrics and Gynecology, NYU of Medicine, 550 First Avenue, New York, NY 10016, USA

(3)

149 E. 33rd St., Apt. 4R, New York, NY 10016, USA

Ana Monteagudo

Email: ana.monteagudo@nyumc.org

Email: josepc02@nyumc.org

Margaret Dziadosz

Email: margaret.dziadosz@nyumc.org

Ilan E. Timor-Tritsch (Corresponding author)

Email: ilan.timor@nyumc.org

Email: josepc02@nyumc.org

Keywords

Anomalies at 11 to 13 6/7 weeksDetection rate of fetal anomalies

Introduction

Seek and you shall find.

Matthew 7:7–11

Detection of fetal anomalies using ultrasound (US) has evolved as the US equipment and probes have evolved. The 18- to 20-week anatomy scan has been part of the routine imaging protocol for the pregnant patient for over 25 years; during this scan most fetal anomalies are detected. However, many of the fetal anomalies seen at the 18- to 20-week anatomy scan are present since the first and/or early second trimesters and if looked for can be detected. Bromley et al. [1] reported a 41.4 % detection rates of malformations at 11 to 13 6/7 weeks without even having a dedicated protocol; furthermore, they were able to diagnose 71 % of the lethal anomalies. Becker and Wegner [2] in a prospective observational study to determine the efficacy of the first-trimester anomaly US scanned 3094 consecutive fetuses between 11 and 13 6/7 weeks with an 83.7 % detection rate of major anomalies [2].

High-frequency transvaginal probes have been the mainstay of early fetal anatomical scanning due to their high frequencies and ability to place the transducer close to the developing fetus. The fact that this early scan has been so dependent on the transvaginal scanning modality is, in our opinion, the main reason why first- and early second-trimester fetal anatomical scanning have not gained popularity. Another, important reason is the lack of understanding of early fetal developmental anatomy and the embryology of many fetal anomalies. On the other hand, recent advances in transabdominal imaging have resulted in high-frequency probes that allow imaging of the first- and early second-trimester fetus and can therefore be used by operators not willing to engage in transvaginal scanning.

The “nuchal scan,” or nuchal translucency (NT) scan, was introduced in the 1990s, and at present approximately 22 % of commercially insured patients and 8 % of publicly insured patients in the USA have the nuchal translucency scan [3]. The NT scan is performed between 11 and 13 6/7 weeks obtaining three sonographic parameters: crown-rump length (CRL), nuchal translucency (NT) measurement, and the presence or absence of the nasal bone (NB). Therefore, the timing of this scan is ideal for a first trimester anatomical survey.

What Normal and/or Abnormal Fetal Structures Can Be Reliably Detected at This Gestational Age?

In 1992, Timor-Tritsch et al. [4] described 97 low-risk patients scanned between 9 and 14 weeks using transvaginal sonography (TVS); the aim of the study was to assess at what gestational age fetal structures such as body contours, long bones, fingers, face, palate, feet, toes, and the four-chamber view could consistently be imaged. The study revealed that by 13–14 weeks all of the structures looked for could be consistently imaged (Table 19.1). Whitlow et al. [5] in 1998 performed a study to determine which was the optimal gestational age to measure the nuchal translucency and at the same time examine the fetal anatomy. They concluded that the best time is at 13 weeks of gestation. Important as well is the fact that with increasing gestational age the percentage of the cases in which anatomy could be seen increased from 75 % at 11 weeks to 98 % at 13 weeks; in addition, they noted that as gestational age increased the need for TVS decreased from 42 % at 11 weeks to 15 % at 13 weeks.

Table 19.1

List of embryonic/fetal structures and the gestational age at which they are always seena

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F femur, H humerus, T tibia, R radius

aModified from ref. [4]

In 2004, Souka et al. [6] published on the feasibility of examining cardiac and non-cardiac fetal anatomy in 1144 low-risk women between 11 and 14 weeks. The scan was performed using both transabdominal sonography (TAS) as well as TVS imaging the following anatomical structures: skull, brain, face, spine, four-chamber and three-vessel views of the heart, stomach, abdominal wall, kidneys, bladder, and extremities. The results revealed that a complete anatomy scan was possible in 48 % of the fetuses. Non-cardiac anatomy was successfully imaged in 86 % of the fetuses. The use of TVS increased the successful examination of fetal anatomy from 72 to 86 % of the fetuses. Transvaginal scanning was particularly helpful in examining the face, kidneys and bladder (Table 19.2). Similarly, to other studies they found that as the crown-rump length increased so did the visualization rates of fetal structures.

Table 19.2

Visualization rates of non-cardiac and cardiac structures with increasing CRLa

CRL (mm)

Non-cardiac (%)

Cardiac

4 ChV (%)

3V (%)

45–54

65

67

25

55–64

84

86

46

65–74

93

93

58

>74

96

97

67

CRL crown-rump length, 4ChV four-chamber view, 3V three-vessel view

aBased on data from ref. [6]

In 2004, Timor-Tritsch et al. [7] tested the ability of a group of American sonographers to successfully perform fetal structural evaluation 11-14 weeks. The results showed comparable detection rates to those reported by European authors. In their prospective cross-sectional study of 223 women between 11 and 13 6/7 weeks, the sonographers were asked to look for fetal structures of the head, neck, spine, heart, abdomen, chest, and extremities targeted 37 fetal structures (Table 19.3). Cases were divided by gestational age into two groups: 11–12 and 13–14 weeks. Similarly to prior studies, as the gestational age increased the number of structures seen increased as well. In this study, the heart structures had the lowest percentage rate of visualization which is not surprising since most practitioners find the fetal heart to be among the most difficult fetal structures to image. The authors concluded that anatomic survey of the fetus between 11 and 14 weeks can be performed by sonographers with good detection rates of most fetal structures.

Table 19.3

Percentage of structures seen at 11–12 and 13–14 weeks by dedicated sonographersa

Structure

11–12 weeks

13–14 weeks

P value

n = 121 (%)

N = 102 (%)

Head and neck

Calvarium

120 (99)

100 (98)

NS

Intracranial anatomy

115 (95)

97 (95)

NS

Lateral ventricles

109 (99)

94 (92)

NS

Choroid plexus

118 (98)

97 (95)

NS

Cerebellum

63 (52)

70 (69)

0.01

Posterior fossa/cisterna magna

67 (55)

73 (72)

0.01

Nuchal anatomy

115 (96)

95 (93)

NS

Lenses

106 (88)

91 (89)

NS

Profile

110 (91)

91 (89)

NS

Nose/lips

86 (71)

81 (79)

NS

Face

89 (74)

85 (83)

0.08

Spine

Cervical

97 (80)

91 (89)

NS

Thoracic

98 (81)

89 (87)

NS

Lumbar

87 (72)

79 (77)

NS

Sacral

42 (35)

49 (48)

NS

Heart

Cardiac axis

86 (71)

75 (73)

NS

4-chamber view

33 (27)

42 (41)

0.03

RVOT

47 (39)

59 (58)

0.04

LVOT

45 (37)

62 (61)

0.0004

Aortic arch

22 (18)

31 (30)

0.03

Ductal arch

18 (15)

24 (24)

NS

Abdomen and chest

Lungs

77 (64)

79 (77)

0.02

Diaphragm

65 (87)

94 (92)

NS

Ventral wall (cord insertion)

117 (97)

98 (96)

NS

Stomach

118 (98)

100 (98)

NS

Kidneys

97 (80)

93 (91)

0.02

Bladder

113 (93)

92 (96)

NS

2 vessels observed by the bladder

102 (84)

92 (90)

NS

Bowel

93 (77)

90 (88)

0.02

Genitalia

39 (32)

51 (50)

0.007

Extremities

Humerus

118 (98)

98 (96)

NS

Radius/ulna

115 (95)

99 (97)

NS

Hand

118 (98)

100 (98)

NS

Fingers

104 (86)

92 (90)

NS

Femur

119 (98)

98 (96)

NS

Tibia/fibula

111 (92)

96 (94)

NS

Foot

117 (97)

95 (93)

NS

aReprinted from American Journal of Obstetrics and Gynecology, 191(4), Timor-Tritsch IE, Bashiri A, Monteagudo A, Arslan AA, Qualified and trained sonographers in the US can perform early fetal anatomy scans between 11 and 14 weeks, 1247–52, Copyright 2004, with permission from Elsevier

In a recent systematic review, Rossi et al. [8] looked at the efficacy of ultrasound between 11 and 14 weeks in the diagnosis of fetal structural malformations. They reviewed 19 articles with 78,002 fetuses undergoing fetal anatomical survey at 11–14 weeks. There were 996 fetuses with malformation with a prevalence of 12 malformations per 1000 fetuses. The overall detection rate of anomalies in this systematic review was 51 %, with detection rates increasing to 62 % when both TAS and TVS were included. Furthermore, the detection rate increased to 65 % among those patients who were at high risk for malformations.

Which Fetal Anatomical Structures Should Be Sought in the Fetal Anatomical Survey at 11 to 13 6/7 Weeks?

Before proceeding, it is important to make one critical clinical important point to keep in mind when scanning the fetus at these gestational ages. Gestational age matters! Not all structures sought during the second trimester (18–22 weeks) scan are completely formed at 11 to 13 6/7 weeks and not all fetal structures “mature” at the same time or at the same gestational age. For example, the fetal brain develops and continually changes during embryonic/fetal life. Depending on the gestational age structures may be deemed normal or pathologic while in reality they did not yet complete their development. For example, in the first trimester a difference of 5–7 days in the gestational age may lead to misdiagnosing a normally developing ventricular structure such as the rhombencephalon as ventriculomegaly or non-visualization of the falx as holoprosencephaly. Therefore, when performing an early fetal anatomical survey, the American Institute of Ultrasound in Medicine (AIUM) [9] list of structures that constitutes a fetal anatomical scan at 18–20 weeks cannot be applied to the fetus at this early gestational age. In 2013 the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) published guidelines [10] as well as a list of suggested structures to be included in the first trimester anatomical survey (Table 19.4).

Table 19.4

Suggested anatomical assessment at time of 11 to 13 + 6-week scana

Organ/anatomical area

Present and/or normal?

Head

Present

Cranial bones

Midline falx

Choroid-plexus-filled ventricles

Neck

Normal appearance

Nuchal translucency thickness (if accepted after informed consent and trained/certified operator available)b

Face

Eyes with lensb

Nasal boneb

Normal profile/mandibleb

Intact lipsb

Spine

Vertebrae (longitudinal and axial)b

Intact overlying skinb

Chest

Symmetrical lung fields

No effusions or masses

Heart

Cardiac regular activity

Four symmetrical chambersb

Abdomen

Stomach present in left upper quadrant

Bladderb

Kidneysb

Abdominal wall

Normal cord insertion

No umbilical defects

Extremities

Four limbs each with three segments

Hands and feet with normal orientationb

Placenta

Size and texture

Cord

Three-vessel cordb

aReprinted from Salomon LJ, Alfirevic Z, Bilardo CM, Chalouhi GE, Ghi T, Kagan KO, et al. ISUOG practice guidelines: performance of first-trimester fetal ultrasound scan. Ultrasound Obstet Gynecol. 2013;41(1):102–13, with permission from John Wiley & Sons

bOptional structures

In this chapter we use the ISUOG list of suggested structures to be imaged at 11 to 13 6/7 weeks (see Table 19.4). Using these guidelines we present fetal anomalies that can be detected at these ages.

Head

Exencephaly–Anencephaly Sequence, Cephalocele

Anomalies that result from failure or abnormal closure of the anterior cranial neuropore at around 26–32 days post conception result in cerebral, spinal or a combined cerebral and spinal defects or dysraphia among these exencephaly–anencephaly sequence, cephaloceles, and spina bifida are among the most common defects with a reported prevalence of 1/1000 pregnancies [11].

The exencephaly–anencephaly sequence is a lethal malformation. In exencephaly the typical sonographic features is acrania in which a relatively well formed brain is seen without the covering fetal cranium (Fig. 19.1). As the pregnancy continues the exposed fetal brain begins to disintegrate eventually, resulting in the typical sonographic features of anencephaly in which the cranium is absent and the fetal orbits prominent. Increasing the US gain the amniotic fluid appears speckled as the result of the sloughing off of the exposed brain tissue (Fig. 19.2) [12]. Reported detection rates at 11 to 13 6/7 weeks are 100 % [813].

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Fig. 19.1

A 10 3/7 weeks fetus with exencephaly–anencephaly sequence. (a) Sagittal view: the normal fetal calvarium is not seen; instead the head appears “flat” and irregular. (b) Coronal view of the fetal head depicting significant amount of brain tissue that has “drooped” to the side of head since it is not confined by the calvarium. (c) 3D reconstruction of the fetus demonstrating exencephaly. (Arrow: abnormal head with absent calvarium.)

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Fig. 19.2

Dichorionic–diamniotic (DCDA) twins at 13 1/7 weeks. (a) The amniotic fluid of twin A appears speckled compared to the amniotic fluid of twin B. (b) Further anatomic evaluation of twin A reveals the typical features of the exencephaly–anencephaly sequence; the head appears irregular and lacks the typical sonographic appearance of the smooth and regular echogenic calvarium (arrow)

Cephalocele is a cranial defect that occurs along the bony sutures, through which brain and/or meninges or a combination of both herniates; this defect is thought to occur as a result of faulty cranial mesoderm development. Recent theories suggest that cephalocele is developmentally and genetically different from exencephaly–anencephaly sequence and should not be considered a neural tube defect [11]. Studies on posterior cephalocele occurring in fetuses with Meckel syndrome have found a relationship with ciliopathy syndromes [11]. Sonographic features are sac-like structures posterior to the head in cases of posterior cephalocele or anterior by the fetal face in cases of an anterior cephalocele (Fig. 19.3). The cephalocele may be small or large. They may contain only meninges (meningocele) or brain tissue (meningomylocele). The larger the cephalocele the more brain tissue it contains, the worse is the prognosis for the fetus. Microcephaly may be seen in as many as 20–25 % of the cases. Reported detection rates at 11 to 13 6/7 weeks are 100 % [8].

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Fig. 19.3

Posterior cephalocele at 12 4/7 weeks. (a) Axial section of the fetal head demonstrating the posterior cranial defect through which brain has herniated into the posterior cephalocele sac (arrow). (b) Sagittal view of the fetal head demonstrating the posterior cranial defect, the cephalocele sac with the brain and midbrain herniating into the sac (arrow). (c) 3D reconstruction of the cephalocele

Holoprosencephaly

During normal fetal development the falx cerebri, a midline structure that separates the single cavity of the forebrain into two hemispheres, should be seen after 9–10 weeks in all normal brains. Lack of visualization of the falx cerebri is consistent with alobar holoprosencephaly (HPE) (Fig. 19.4). At 11 to 13 6/7 weeks the choroid plexus is seen on each side of the midline falx; this configuration has been likened to a butterfly with the wings open [14] (see Fig. 19.4a). Using the “butterfly sign” Sepulveda et al. [15] screened 11,068 live fetuses for HPE over a 9-year period. Among this cohort they diagnosed 11 cases of HPE, which demonstrated lack of visualization of the “butterfly sign.” Detection rate of HPE using the absent “butterfly sign” was 100 %. In addition, they noted that 40 % had a biparietal-diameter less than the fifth centile for gestational age (GA); which further aided in the diagnosis.

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Fig. 19.4

A composite image of a normal brain and four cases of holoprosencephaly. (a) Axial section of a normal fetus at 13 2/7 weeks for comparison, displaying the midline falx cerebri which divides the brain into the right and left hemispheres; the echogenic choroid plexus is seen to each side of the falx (Arrow=Falx). This appearance has been likened to a butterfly with open wings. (b) Fetus with HPE at 9 6/7 weeks. (c) Fetus with HPE at 11 4/7 weeks. (d) Fetus with HPE at 12 1/7 weeks. (e) Fetus with HPE at 13 2/7 weeks. The common sonographic feature of all four fetuses with holoprosencephaly imaged in an axial view is the absent falx; single ventricular cavity; choroid plexus superior to the fused thalami; and absence of the normal “butterfly” appearance of the axial view

Holoprosencephaly is a common malformation involving the forebrain; this malformation results from complete or incomplete failure of the forebrain to divide during the second to the third week post-conception [1618]. The prevalence of holoprosencephaly at 11 to 13 6/7 weeks has been reported as 1:1300 pregnancies; with approximately 66 % having a chromosomal abnormality of which 86 % have trisomy 13 and 4 % trisomy 18 [19]. This anomaly has a spectrum ranging from the most severe alobar HPE, to semilobar HPE, and to lobar HPE and the least severe middle interhemispheric variant (MIHV). In approximately 80 % of individuals affected with HPE [9] a craniofacial anomaly is also present [16]. The craniofacial anomalies range from cyclopia (single midline eye), synophthalmia (partial midline face fusion of the two eye), and a proboscis (nasal appendage with a single nostril located above the eyes) [17]. During the first trimester, most of the cases of HPE that are diagnosed are alobar; although the semilobar type can also be diagnosed; however, at 11 to 13 6/7 weeks, this presents a challenging task. Three-dimensional inversion rendering can be used to differentiate between a normal brain and HPE; this can be used as an additional tool in the diagnosis of HPE in the first trimester [20] (Fig. 19.5). Lobar HPE, which is a more subtle malformation and depends upon the appearance of the cava is diagnosed at or after the 18- to 20-week anatomy scan. Most fetuses affected by HPE do not survive. Detection rates of 50–100 % have been reported [813].

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Fig. 19.5

Three-dimensional display of the three orthogonal scanning planes (axial, coronal, and sagittal) as well as the inversion mode; in which the anechoic cerebral spinal fluid is “inverted” and displayed as an echogenic structure in a fetus with trisomy 13 at 13 5/7 weeks with alobar HPE. (a) Coronal section showing the single or “mono” ventricle; absence of the midline structures and fused thalami. (b) Sagittal view of the fetus; the face is facing the left side of the picture; the head contains fluid. (c) Axial section showing similar features described in (a). Box 3D depicts the inverted image of the fluid contained within the single brain ventricle

Neck

Thickened Nuchal Translucency and Cystic Hygroma

The significance of thickened or increased nuchal translucency (NT) in the screening for aneuploidies, congenital heart defects and other malformations is well established. Thickened NT refers to a measurement that is greater than the 95th centile; which in turn increases with gestational age and is just about 2.5 mm; in contrast, its 99th centile is fixed at 3.5 mm (Fig. 19.6) [2122]. A thickened NT in itself is not an abnormality since it can be seen in both normal pregnancies as well as those with pathologies. Kagan et al. [23] looked at the relationship between thickened NT and chromosomal defect. With increasing NT from the 95th centile to 3.4 mm the incidence of chromosomal aneuploidy was 7 %; at an NT of 3.5–4.4 mm the incidence of chromosomal aneuploidy was 20 %; at a NT of 4.5–5.4 mm it was 45 %; at a NT of 5.5–6.4 mm, 50 %; at a NT of 6.5–7.4 mm, 70 %; and with NT of ≥8.5 mm, 75 %. Another interesting finding was that about half of the fetuses with trisomy 21 has NTs ≤ 4.5 mm; NT greater than 4.5 mm was seen in about 60 % of the cases with trisomy 13, 75 % of fetuses with trisomy 18 and 90 % of cases of Turner syndrome; moreover, fetuses with Turner tended to have the thickest NT ≥ 8.5 mm.

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Fig. 19.6

Fetus at 11 5/7 weeks demonstrating NT of 3.1 mm; at this gestational age this measurement falls above the 95th centile

In euploid fetuses with thickened NT the association with congenital heart defects (CHD) is well known. In a 2003 meta-analysis by Makrydinas et al. [24] an NT > 95th centile had a sensitivity of 37 % and specificity of 96.6 %; and for NT > 99th centile they were 31 % and of 98.7 %, respectively, with a positive likelihood ratio of 24 for the diagnosis of major congenital heart defect [2124]. In a subsequent 2013 meta-analysis by Sotiriadis et al. [25] they found that approximately 45 % of chromosomally normal fetuses with CHD had an NT > 95th and 20 % had an NT > 99th centile.

Cystic hygroma refers to bilateral, septated, cystic, fluid-filled spaces located in the occipitocervical region [26]. This is a result of obstruction between the lymphatic and venous vessels in the neck resulting in accumulation of lymph in the jugular lymphatic sacs (Fig. 19.7). In fetuses with cystic hygroma between 11 and 13 6/7 weeks approximately 51 % [27] to 54.9 % [28] will have a chromosomal abnormality; of which trisomy 21 is the most common. In a recent retrospective cohort study of 944 fetuses with first trimester cystic hygroma; the prevalence of trisomy 21 was 21.4 %; followed by monosomy X (Turner syndrome) 12.1 %, trisomy 18 at 11.4 % and trisomy 13 at 3.6 % and other karyotypic abnormalities such as other trisomies, deletions, duplications, unbalanced translocations, inversions, and sex chromosome abnormalities [28]. Among the fetuses with normal karyotype 28.8 % had a major anomaly. Urinary, central nervous system, and cardiac were the most common accounting for 15 % of the anomalies [28]. In the same cohort six fetuses had genetic syndromes; Angelman and Noonan syndrome were among the genetic syndromes seen. Perinatal loss occurred in 39 % of ongoing pregnancies and the overall abnormal outcome ensued in 86.6 % of the fetuses [28].

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Fig. 19.7

Fetus at 12 3/7 weeks with cystic hygroma. (a) Posterior coronal section showing the bilateral cystic dilatation at the level of the posterior neck area (arrow). This pathology is a result of obstruction between the lymphatic and venous vessels in the neck resulting in accumulation of lymph in the jugular lymphatic sacs. (b) Sagittal view of the fetus showing extensive posterior hygroma and the total body edema. (c) 3D reconstruction of cystic hygroma

Face

Absent Nasal Bone, Cleft Lip ± Palate, Cataracts, Micrognathia

During the early anatomical survey, similarly to the traditional second trimester anatomical survey, a profile view of the face should be obtained. This may reveal an absent or hypoplastic nasal bone, a cleft lip and/or palate, or micrognathia.

Absent nasal bone is not a fetal malformation per se however it is a marker of fetal aneuploidy; specifically of the common trisomies (Fig. 19.8). The nasal bones are actually paired structures, there is a right and a left nasal bone, and there can be unilateral as well as bilateral absence or hypoplasia. Absent nasal bone is seen in 60 % of fetuses with trisomy 21, 53 % of trisomy 18 and in 45 % of trisomy 13; its absence confers a likelihood ratio of 27.8 for Down syndrome; furthermore, it can be seen in 2.5 % of euploid fetuses [29]. Among euploid pregnancies absent nasal bone is seen more frequently in African American women (5.8 %) than in white women (2.6 %) or Asian women (2.1 %) [30]. In a recent publication among 57 fetuses with absent nasal bone and normal karyotype three fetuses had an adverse outcome and, in all, additional sonographic abnormalities were seen [30].

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Fig. 19.8

Two fetuses are seen, one with a normal and one with absent nasal bone and cystic hygroma. To image the nasal bone or its absence it is important to obtain the correct sagittal scanning plane of the face which shows the tip of the nose (long arrow) and the palate (short arrow). (a) Fetus at 12 1/7 weeks with a normal-appearing nasal bone. (b) Fetus with absent nasal bone at 13 6/7 weeks

Cleft lip and/or palate (CLP) is a common facial anomaly with a reported incidence of 1.7 per 1000 live births; however, ethnic and geographic variation exist [31]. In up to 80 % of the cases cleft lip is unilateral, typically affecting the left side and most of the affected fetuses are male. However, isolated cleft palate is more commonly seen in females with a reported incidence of 1 in 2500 live births [31]. During development, a continuous upper lip is formed by 8 weeks when the medial nasal and maxillary processes fuse. Failure of fusion of the medial nasal and maxillary processes will result in a cleft lip affecting one or both sides. The palate develops from the primary and the secondary palate. Its development starts at 7 weeks, but is not completed until the 14th week. At 11 to 13 6/7 weeks a sagittal, coronal, and axial view using 2D and 3D sonography can detect a CLP (Fig. 19.9). In cases of bilateral cleft lip and palate a protuberance is seen anterior to the lips in the sagittal plane; in the axial plane the cleft lip and palate can be seen as a deep indentation. Three-dimensional ultrasound, specifically 3D reconstruction of the face using the coronal plane can help in evaluating the facial defects (see Fig. 19.9b). Detection rates of CLP in the first trimester are low, ranging from 5 to 50 % [813]. The retronasal triangle (see Fig. 19.9e) can be imaged, using 2D or 3D sonography, by obtaining an anterior coronal view of the fetal face. The apex of the retronasal triangle is made up of the two nasal bones, the sides are the frontal process of the maxilla and the base of the triangle is the primary palate [32]. In cases of CLP, a defect can be imaged at the base of the triangle, at the site of the palate (Fig. 19.9b Box C) Boc C. The retronasal triangle view likely can improve the detection and diagnostic rates of CLP; however, no large prospective studies looking at efficacy of the retronasal triangle are available to date. Furthermore, this view has recently been reported as a new way to evaluate the presence or absence of the nasal bones [3234].

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Fig. 19.9

Fetus with unilateral left-sided cleft lip and palate at 12 5/7 weeks. (a) Axial section through the upper lip of a fetus with unilateral cleft lip and palate diagnosed at the time of the nuchal translucency scan (arrow). (b) 3D orthogonal planes of the same fetus. Box A: a sagittal view of the face. Upper Left Box B: a coronal section showing the abnormal retronasal triangle with a gap at the area of the left side of the palate (arrow). Lower Left Box C: the axial section; arrow points to defect (c) 3D reconstruction of the fetus with the unilateral cleft lip and palate (arrow). (de) 2D and 3D thick slices of a normal retronasal triangle

Cataracts: the reported incidence is 1–6/10,000 births [35]. The fetal lens develops from the surface ectoderm before the sixth week of gestation [35]. Fetal cataracts may be the result of a very early in-utero fetal infection, such as rubella, varicella, herpes and CMV, exposure to a toxin (anti-psychotic drugs such as carbamazepine), idiopathic or genetic. A genetic cause is seen in 30 % of unilateral cases and in 50 % of bilateral cases [35]; genetic causes includes syndromes such as Walker–Warburg syndrome and karyotypic abnormalities such as trisomy 21, 18, and 13. The normal sonographic appearance of the fetal lens is that of a ring with an anechoic center and an outer echogenic rim (Fig. 19.10a). At times the hyaloid artery can be seen as a linear structure between the posterior aspect of the lens and the optic disc; however, the hyaloid artery typically regresses before birth. In fetal cataracts there is opacification of the anechoic center-core of the lens; at times, in conjunction with cataracts, there may be reduction in the size of the fetal eyes [36] (see Fig. 19.10b).

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Fig. 19.10

Axial section of the fetal face at the level of the fetal orbits. (a) Normal fetus within the orbits the normal lenses are seen. The sonographic appearance of a normal lens is that of an echoic ring with a central sonolucency (arrows). (b) Axial section of a fetus with autosomal dominant cataracts at 12 5/7 weeks. Within the normal orbits, the ring-like appearance of the lens is lost and replaced by a ring filled with a central echogenic material, the cataract. The arrow points to the small and receding jaw

The mandibular process forms the lower jaw, lip and chin at around 8–12 weeks; with final fusion of all of the parts that will form the mandible completed by 13 weeks of pregnancy. Normal development of the mandible can be disrupted as the result of genetic syndromes or environmental exposures [37]. Micrognathia is a common feature of over 100 genetic conditions such as Treacher Collins, Robin sequence, fetal akinesia syndrome, and chromosomal aneuploidy such as Trisomies 18 and 13 as well as deletions [3738]. As stated by Paladini in 2010 [37] fetal micrognathia is almost always an ominous finding; therefore, when seen, a detailed work up is essential. Using 2D and 3D US, the normal fetal mandible can be imaged in the sagittal plane when obtaining the profile, in an axial view at the level of the mandible or as part of the 3D image of the face (Fig. 19.11a). The diagnosis of micrognathia can rely on subjective assessment or using objective methods such as the jaw index and inferior facial angle. When applying these indexes to fetuses at 11 to 13 6/7 weeks, it is important to remember that they were developed based on fetuses at 18–20 weeks and have not been validated to be used at an earlier gestational age [3738] (see Fig. 19.11b).

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Fig. 19.11

Sagittal view of the fetal profile. (a) Normal fetal profile. (bc) Slightly different views of the profile of a 13 6/7 weeks fetus with micrognathia and a thick NT. The fetus was a carrier of an unbalanced deletion (arrow=jaw)

Spine

Open Spina Bifida

At 11 to 13 6/7 weeks the fetal spine can be assessed in the sagittal, coronal, and axial planes in a similar fashion as it is routinely performed later during the second-trimester anatomical survey. In the second trimester the diagnosis of open spina bifida relies on several sonographic markers: (1) the presence of a bulge or irregularities of the spine; (2) two established and sensitive cranial findings the “lemon sign” and “banana sign.” Open spina bifida can be diagnosed at 11 to 13 6/7 weeks or earlier by observing a bulge or disruption of the bony spine and skin in the sagittal plane (Fig. 19.12a, b) [3940]. The sonographic detection of the “banana and lemon” signs has been reported in fetuses after the 12th week of pregnancy [3941]. In pregnancies 12 weeks or less, the cerebellum may just appear slightly convex; but the typical appearance of the “banana sign” can be consistently demonstrated after the 12th week [41]. Recent research in this area has resulted in several additional cranial sonographic findings that have been developed specifically to screen fetuses at 11 to 13 6/7 weeks, especially open spina bifida. The signs include: non-visualization of the intracranial translucency (IT) [42] (see Fig. 19.12c, d), increasing brain stem diameter to brain-stem-to-occipital bone distance (BS/BSOB) [43] and cisterna magna width < 5th [44]; as well as in the axial plane the biparietal diameter (BPD) measurement of <5th centile [4546] and biparietal-to-transverse abdominal diameter ratio of ≤1 (BPD/TA) [47]. Fetuses “screen positive” for these new cranial sonographic markers should be referred to centers with expertise in scanning the early pregnancy. Most of these new cranial sonographic signs can be looked for in the median view of the fetal face, the same plane used to measure the nuchal translucency. At present, there is limited data regarding the performance of these new cranial signs for the detection of open spina bifida; however, Bernard et al. [45] reported that using a BPD of <5th percentile could detect 50 % of the cases of open spina bifida by selecting about 5 % of the cases for further expert scanning.

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Fig. 19.12

Sagittal image of the fetal spine in at 12 3/7 weeks with a lumbosacral open spina bifida. This finding was confirmed during subsequent studies as well as postnatally. (a) The lumbosacral spinal defect is seen at the arrow. (b) Sagittal view, slightly off the midline, demonstrating the myelomeningocele sac as well as the defect of the vertebral bodies. (c) Sagittal view of the fetal head demonstrating lack of visualization of the intracranial translucency. (d) Sagittal view of a normal fetus demonstrating the normal intracranial translucency (IT). The IT is seen between the brainstem (Bs) and the choroid plexus (Cp). Th = thalamus

Heart

The Abnormal Heart

Congenital heart defect (CHD) is a common anomaly with a reported incidence of 8–10/1000 live births [48]. Currently, detection rates of CHD in the first trimester remain relatively low with the exception of several centers with expertise in first trimester fetal echocardiography. There are many factors that play a significant role in the detection of heart anomalies such as experience in fetal echocardiography, maternal body habitus, equipment quality, and liberal use of transvaginal sonography. The association between a thickened NT and CHD is well documented in the literature and was touched on before [2124]. In a recent meta-analysis [25] the pooled sensitivity, specificity, LR+, and LR− for NT > 95th was 44.4, 94.5, 7.49, and 0.63 and for an NT > 99th it was 19.5, 99.1, 21, and 0.83, respectively. Of lately, the abnormal ductus venosus flow and tricuspic regurgitation have emerged as important additional sonographic clues when screening for congenital heart defects at 11 to 13 6/7 weeks. In a recent prospective study, reversed a-wave in the ductus venosus was seen in 28.2 % of fetuses with CHD compared to 2.1 % of fetuses with no cardiac disease. When both reverse a-wave and NT > 99th centile were present, CHD was seen in 38.8 % and for NT > 95th centile 47.1 % [49]. In a publication from 2011 tricuspid regurgitation was seen in 32.9 % of euploid fetuses with cardiac disease and 1.3 % of fetuses with no cardiac disease; any one of the three markers (thick NT, reversed a-wave, tricuspid regurgitation) was seen in 57.6 % of fetuses with CHD and in 8 % of fetuses without cardiac disease [50]. Among the cardiac anomalies that can be detected after fetal echocardiography in the first trimester are hypoplastic left heart, double outlet right ventricle, and tetralogy of Fallot; detection rates ranges from 50 to 99 % [8] (Fig. 19.13).

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Fig. 19.13

Four-chamber view of the fetal heart. (a) Normal four-chamber view of a fetus at 13 3/7 weeks. (b) Four-chamber view with power Doppler applied showing normal blood flow through both atrioventricular valves. (c) Fetus at 13 weeks with the suspected diagnosis of atrioventricular canal (AV canal) or atrioventricular septal defect (AVSD) defect (arrow); the crux of the heart appears abnormal and the two valves cannot be clearly identified

Chest

Congenital Diaphragmatic Hernia

When evaluating the fetal chest in the first trimester, symmetry of the lung fields and absence of effusions or masses are the key markers of a normal chest. The normal heart is nestled between the lungs, the apex points to the left and approximately two-thirds of the heart is in the left side of the chest (see Fig. 19.13a, b). When the normal position of the heart is disrupted and the heart is pushed either to the right or left, the presence of a chest mass must be entertained. In congenital diaphragmatic hernia the fetal stomach and/or bowel is seen in the chest in the transverse section of the chest (Fig. 19.14). The heart and the mediastinum may be minimally or significantly displaced laterally to the right or the left chest depending on the side of the diaphragmatic defect. The reported prevalence of congenital diaphragmatic hernia (CDH) is 1 in 2500 to 1 in 3500 live births; with hernias involving the left diaphragm more common than right-sided, with a ratio of 6:1 [51]. Although bilateral hernias have been reported, they are fatal [51]. In 90 % the defect is posterolateral (Bochdalek hernia), 9 % anterior-medial (Morgagni hernia) and the remainder encompasses unusual forms of diaphragmatic defects [51]. In nearly 40 % of the fetuses with CDH, an increased nuchal translucency is seen between 11 and 13 6/7 weeks; the increase in NT may be an early sonographic sign of intrathoracic compression-related pulmonary hypoplasia [52]. Diagnosis of CDH at 11 to 13 6/7 weeks is challenging and even when the NT is increased, detection rates are about 50 % [13]. At present most CDHs are diagnosed later in pregnancy and small defects may only be diagnosed postnatally.

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Fig. 19.14

View of the fetal chest at the level of the four chambers; the heart is seen pushed to the right side of the image and in the left side the fetal stomach St is seen. The fetal stomach should never be seen at the same time as the four chambers of the heart (H)—when this is seen the diagnosis is CDH until proven otherwise

Abdomen

Kidneys

The normal fetal kidneys can be imaged at 11 to 13 6/7 weeks. In 2004, our group reported on visualization rates of different fetal structures on scans performed by sonographers [7]. Visualization rates of the normal kidneys and bladder at 11–12 weeks was 80 % and 93 %, respectively; and at 13–14 weeks, 91 % and 96 %, respectively. The normal kidneys at this gestational age appear relatively hyperechoic when compared to the sonographic appearance of kidneys later in the pregnancy. By using color/power Doppler to visualize the renal arteries, one can enhance finding and imaging of the kidneys at this gestational age. The adrenal glands at this gestational age are relatively large, compared to the neighboring kidneys and sonographically are anechoic, as they are also later in pregnancy. Diagnosis of unilateral or bilateral renal agenesis is a difficult diagnosis with detection rates of <20 % in the first trimester [13].

Megacystis

Megacystis is defined as a longitudinal diameter of the fetal bladder of ≥7 mm [19] (Fig. 19.15). In the study of Kagan et al. [19], the reported prevalence at 11 to 13 6/7 weeks was 1:1632 pregnancies, with an incidence of aneuploidy of 31 %. Among the chromosomal aneuploidies, Trisomies 13 and 18 were the most commonly seen abnormality, accounting for 54.5 % and 36.4 %; trisomy 21 was seen in 9.1 % of the cases [19]. Among the majority (68.6 %) of euploid fetuses with megacystis, the bladder was ≤15 mm and spontaneous resolution occurred in 90 % by 16 weeks, resulting in healthy newborns. In two cases there was progression to obstructive uropathy. There were four cases with megacystis with the bladder measuring more than ≥15 mm and these pregnancies were terminated. Megacystis is a relatively easy diagnosis in the first trimester and 100 % detection rates have been reported [13].

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Fig. 19.15

Fetus with megacystis at 12 4/7 weeks. (a) On the sagittal view the megacystis is seen filling the fetal pelvis extending into the abdomen. (b) A 3D reconstruction of the fetus with megacystis. (cd) Transverse section at the level of the large bladder; using power Doppler demonstrates the two umbilical arteries flanking the bladder confirming the diagnosis

Abdominal Wall

Gastroschisis, Omphalocele, Limb-Body Wall Complex, OEIS (Omphalocele–Exstrophy–Imperforate Anus–Spinal Defects), Pentalogy of Cantrell

Gastroschisis is an abdominal wall defect, typically to the right of the umbilical cord through which herniation of intestinal organs occur (Fig. 19.16). Gastroschisis can be reliably diagnosed at 11 to 13 6/7 weeks with reported detection rates of 50–100 % [813]. Nuchal translucency > 95th centile has been reported in approximately 10 % of the cases [13]. In a recent international study [53], approximately 85 % of the cases of gastroschisis were isolated defects; chromosomal syndromes were seen in 1.2 %, with Trisomies 18, 13, sex chromosomes and trisomy 21 being the most common.

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Fig. 19.16

Fetus at 13 0/7 weeks with gastroschisis. (a) Sagittal view showing the free floating bowel in the lower abdomen (arrow). (b) Transverse view at the level of the abdominal wall defect clearly demonstrating the free loops of bowel anterior to the abdomen (arrow). (c) Using power Doppler the two umbilical vessels are seen, to the right of the umbilical cord insertion the bowel is seen outside the abdominal cavity (arrow)

Omphalocele is a midline abdominal wall defect, at the level of the umbilical cord insertion into the abdomen, through which bowel alone or bowel and liver herniate into a peritoneal sac (Figs. 19.17 and 19.18). The bowel-containing omphalocele can be reliably diagnosed only after the 12th week of the pregnancy. This is due to the fact that the omphalocele containing bowel only may be difficult to differentiate from the physiologic midgut herniation which occurs between 8 and 11 weeks. A pathology has to be considered only after failure of the physiologically herniated bowel loops to return to the abdomen. It is important to note that upwards of 20 % of fetuses do not complete this physiologic replacement as late as 12 completed weeks. This delay is seen more frequently in aneuploid gestations [54].

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Fig. 19.17

Fetus at 12 5/7 weeks with a large liver-containing omphalocele and a cystic hygroma. (a) Sagittal view of the fetus showing the large liver-containing omphalocele. (b) 3D rendering of the omphalocele. (c) Transverse view through the abdomen at the level of the omphalocele. (d) Using color Doppler the fetal heart is seen “pulled inferiorly” almost through the abdominal defect into the omphalocele sac

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Fig. 19.18

Fetus with a liver-containing omphalocele at 12 weeks. (a) Sagittal view of the fetus showing the liver-containing omphalocele. (b) Transvaginal transverse section of the omphalocele sac reveals the liver (L), bowel (B), and the stomach (St) within the sac. (c) 3D reconstruction of the liver-containing omphalocele. Note that in comparison to the gastroschisis, this defect is enveloped in a peritoneal sac and the outer surface is smooth

In a large screening study at 11 to 13 6/7 weeks, the incidence of bowel-containing omphalocele was dependent on the CRL with a prevalence of 1:98 for a CRL of 45–54.9 mm; 1:798 for a CRL of 55–64.9 mm to 1:2073 for CRL 65–84 mm [19]. In our opinion, the high incidence of bowel-containing omphalocele at the smaller CRLs is due to the fact that cases of physiologic midgut herniation were called omphalocele. In contrast, the prevalence of liver-containing omphalocele was 1:3360 [19]. Fifty-five percent of the bowel-containing omphaloceles had a chromosomal abnormality, with trisomy 18 (56.8 %) being the most common, followed by trisomy 13 (25.7 %), monosomy x (45 XO or Turner syndrome) (8.1 %), and trisomy 21 (4.1 %). Of the liver-containing omphaloceles, 52.9 % had a chromosomal abnormality of which trisomy 18 accounted for 66.7 % and trisomy 13 for 33.3 %. In these cases, though normal nuchal translucency (NT) presents a risk of aneuploidy of 28 %, as the NT measurement increases, there is a direct correlation with a steady increasing likelihood of aneuploidy [195556]. Omphalocele is also associated with other malformations and syndromes including Beckwith-Wiedemann syndrome, neural tube defects and diaphragmatic defects. Postnatal complications are related not only to aneuploidy type but also to size of the defect and extent of liver herniation [57].

Limb-body wall complexOEIS syndrome, and Pentalogy of Cantrell are rare major abdominal wall defects. Limb-body wall complex is a uncommon defect in which at least three of the following defects are present: exencephaly/encephalocele with facial clefts; thoraco-abdominoschisis/ventral body wall defect and limb defects [58]. Russo et al. [59] has proposed that there are two clearly distinguishable phenotypes: “placento-cranial” and “placento-abdominal.” The “placento-cranial defects” are characterized by encephalocele or exencephaly always associated with facial clefts and amniotic band between the cranial defects and placenta. The second phenotype, the “placento-abdominal defects,” has urogenital anomalies, anal atresia, lumbosacral meningocele, and placental anomalies such as presence of short cord, persistence of extraembryonic coelom, and intact amnion (Fig. 19.19).

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Fig. 19.19

Fetus at 11 1/7 weeks with the limb-body wall complex; sonography most consistent with placenta-abdominal type. (a) The amnion (arrow) is seen closely surrounding the fetus consistent with oligohydramnios; the liver (L) is seen extracorporeally with no distinct membrane covering. (b) The fetus is essentially attached to the placenta (P) by the very short umbilical cord. Power Doppler demonstrates the short cord. (c) Transverse section at the level of the abdominal wall defect reveals the extracorporeal liver (L) and the amnion, which is closely applied to the fetal body (arrow). (d) 3D reconstruction depicting the abdominal wall defect and of the lower extremity deformity

OEIS syndrome is a rare condition with a prevalence of 1: 200,000–1:400,000 pregnancies. The pathogenesis remains largely unknown [60]. The typical findings are omphalocele, exstrophy of cloaca, imperforate anus and spinal defect; other malformations such as renal, single umbilical artery and limb defects are commonly seen with OEIS [61].

Bladder exstrophy can be identified in the first trimester as a large, lower abdominal wall cystic mass, lack of visualization of an intra-abdominal bladder, low umbilical cord insertion as well as the presence of umbilical cord cysts [62] (Fig. 19.20). Later in the second trimester the large cystic lower abdominal mass disappears, as the exstrophied bladder ruptures and results in a hyperechoic lower abdominal wall bulge, with lack of visualization of an intra-abdominal bladder. The umbilical cord cysts may or may not be seen as the pregnancy progresses. Additional features include an abnormally small phallus with anteriorly displaced scrotum [63]. Bladder exstrophy is more common in males than in females and, in addition to the bladder defect, there is also an abdominal wall, pelvic floor, and bony pelvis defect. Sensitivity of early detection is low without associated findings and potential mimicking of bladder presence through presence of a urachal cyst [546465]. It can be associated with the aforementioned OEIS complex or cloacal malformation. Various associated anomalies include renal, neural tube defects, omphalocele, hydrocolpos, umbilical cord cysts, and separated pubic bones [6466].

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Fig. 19.20

Fetus at 11 5/7 weeks with exstrophy of the bladder and umbilical cord cysts. (a) Sagittal view of the fetus shows a large cystic lower abdominal wall mass, the fetal bladder at the same time; no fetal bladder was identified within the pelvis. (b) 3D reconstruction of exstrophy of the bladder. (c) Transverse section at the level of the exstrophied and dilated bladder is seen; using color Doppler a single umbilical cord was seen. (d) The umbilical cord reveals two cord cysts; cord cysts are often seen with exstrophy of the bladder

Pentalogy of Cantrell is another rare condition with prevalence ranging from 1:65,000 to 200,000 with five anomalies that encompass this malformation: (1) a median supraumbilical abdominal wall defect; (2) a defect of the lower sternum; (3) a deficiency of the anterior diaphragm; (4) a defect of the diaphragmatic pericardium; and (5) intracardiac defects [67]. This sequence may result in ectopia cordis as well as an omphalocele but other intra-abdominal structures may also be seen as extra-corporal (Fig. 19.21). This condition has been associated with the common trisomies (21, 18, and 13).

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Fig. 19.21

Fetus at 9 1/7 weeks with ectopia cordis and omphalocele. (a) Sagittal view of the fetus showing the heart pulsating outside the fetal thorax as well as a liver-containing omphalocele. (b) Using color Doppler the fetal heart is seen to be protruding through the chest. Given the other anomalies this fetus likely had Pentalogy of Cantrell; fetal karyotype revealed trisomy 16. Courtesy of Patricia Mayberry, RDMS

Extremities

Hand Malformations, Polydactyly, Sirenomelia

In the first trimester it is possible to accurately identify and measure the three components of the extremities. In the upper limbs these are: arms (humerus), forearms (ulna, radius), and hands; in the lower extremities the thighs (femur), legs (tibia, fibula), and feet. Their detection rate is in greater than 95 % of the cases [6869]. Our group reported detection rates of over 97 % for the upper extremity and over 95 % for the lower extremities [7] (Fig. 19.22). Detection rate of limb anomalies may be low, if they are isolated findings. Gray et al. [70] enrolled 100 patients with congenital upper extremity reduction or duplication anomalies and reviewed their prenatal records. Prenatal diagnosis was made in 31 % of the cases. In a recent study, Bromley et al. [1] reported a 38.8 % detection rate of anomalies involving the extremities at ≤14 weeks, although they did not have a defined imaging protocol.

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Fig. 19.22

Fetus at 12 5/7 weeks. (a) The normal upper extremity is seen demonstrating the three components of the limb the humerus, radius/ulna, and hand. (b) The two lower extremities are seen. (c) 3D reconstruction of the fetus showing the normal upper and lower extremities

Limb anomalies have a prevalence of approximately 6/10,000 live births; with a higher occurrence of anomalies occurring in the upper limbs. Unilateral limb anomalies are more common than bilateral and the right side is more likely to be affected than the left side [71]. In a study looking at forearm anomalies 9 of the 66 were diagnosed between 11 and 13 6/7 week; 29.7 % had a chromosomal aneuploidy of which trisomy 18 was the most common abnormality; 29.7 % had genetic syndromes such as Cornelia de Lange and VATER syndrome; the anomalies were isolated in 23 % [72] (Fig. 19.23).

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Fig. 19.23

A composite image of several fetuses with different upper extremity abnormalities. (a) Fetus at 13 5/7 weeks demonstrating bilateral clubbing of the hands, fetal karyotype was consistent with trisomy 18. (b) 3D reconstruction of the clubbed hands of the fetus with trisomy 18. (c) Fetus at 14 weeks with ectrodactyly (split hand). (d) Fetus at 14 weeks with post-axial polydactyly. (eg) Multiple views of a fetus at 11 weeks with ectrodactyly

Sirenomelia (mermaid syndrome) is a rare and fatal condition of uncertain etiology; the condition is characterized by fusion of the lower extremities resulting in a single limb. Other anomalies seen are urogenital, gastrointestinal and single umbilical cord (Fig. 19.24) [73].

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Fig. 19.24

Fetus at 12 weeks with sirenomelia. (ab) are targeted views of the single fused lower extremities. (c) 3D reconstruction of the sirenomelia

The Placenta

Subchorionic Hematoma, Placental Attachment Disorders

In the first trimester, subchorionic hematomas may be seen as crescent shaped anechoic or hypoechoic regions at the placento-decidual interface. This disruption may occur due to inherent placental dysfunction with controversial, but likely somewhat increased risks of placental abruption and preterm premature rupture of membranes. Subchorionic hematomas are relatively common findings during the first-trimester scan with reported incidence of 0.5–22 % [74]. When the size of the hematoma measures greater than 25 % of the gestational sac size, there was a twofold increased risk of pregnancy loss [74]. In addition, retroplacental hematomas render a higher risk to pregnancy outcome than do marginal bleeds [75] (Fig. 19.25).

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Fig. 19.25

Subchorionic hematoma in a fetus at 13 weeks; the smaller arrow point to the hematoma which is large but does not involve the placenta (large arrow)

It is critical to evaluate the implantation site in order to identify morbidly adherent placentas or cesarean scar pregnancies. Please refer to Chap. 17 for further discussion.

Umbilical Cord

Two-Vessel Cord

The normal umbilical cord contains one vein and two arteries and can be identified in the first trimester. The two arteries can be identified by color or power Doppler mode by indirect inference, imaging the vessels bilaterally bordering the fetal bladder wall on the pelvic cross-section. Due to ease and speed of obtaining this image, the ALARA principle is not compromised. A two-vessel cord implies the presence of a single umbilical artery (SUA). This anomaly is one of the most common ultrasonographic findings in pregnancy; it is seen in 0.5 % to upwards of 6 % of singleton gestations with a sensitivity quoted between 57.1 and 84.2 and specificity of 98.9–99.8 in the first trimester [7678]. Incidence increases three to four times in twin gestations [7879]. SUA is associated with congenital malformations and chromosomal aneuploidies in 10 % of cases [80], but also preterm birth, growth restriction, and poor fetal outcomes [78]. Congenital malformations are identified during first trimester scans in 17 % of cases, with an additional 7 % found during the second trimester [77]. The majority of malformations associated with SUA is genitourinary or cardiac in nature, but may also include congenital diaphragmatic hernias, musculoskeletal anomalies, exstrophy of cloaca sequence, sirenomelia, or VATER syndrome [8183] (Fig. 19.26).

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Fig. 19.26

First-trimester single umbilical artery. (a) Using color Doppler only a single artery is seen flanking the fetal bladder in a fetus at 11 6/7 weeks. (b) The umbilical cord insertion into the placenta is seen in a 11 5/7 weeks pregnancy with the single umbilical artery

Summary

In 2014 a consensus statement on fetal imaging was published [84]. This statement went on to say that “Offering first-trimester screening for aneuploidy assessment at 11 to 13 6/7 weeks of gestation is recommended by the American College of Obstetricians and Gynecologists. If a late first trimester ultrasonography is performed for dating or nuchal translucency assessment, evaluation for early detection of severe fetal anomalies such as anencephaly and limb-body wall complex is reasonable. In some experienced centers, detection of other major fetal anomalies in the first trimester is possible” [84]. This statement brought to the forefront the fact that fetal anomalies can be detected in the first trimester. The goal of this chapter was to further raise awareness and to promote the reality that first trimester anatomy scan and detection of fetal anomalies at the time of the “nuchal scan” is feasible and should be strongly considered even in the era of increasing use of noninvasive prenatal diagnosis. Also it is important to realize that a significant number of fetal anomalies can be diagnosed reliably. The most important information is that diagnosis of lethal and major anomalies have very high detection rates and, in some studies, this number is as high as 100 % for anomalies such as exencephaly–anencephaly sequence, cephalocele, holoprosencephaly, and megacystis. During the “nuchal scan” it is important not only to correctly measure the NT and assess the nasal bone, but to look at the rest of the fetus. “Search for fetal anomalies and you shall find them.”

Teaching Points

·               The detection of fetal anomalies in the first trimester is possible.

·               When anomalies are looked for in a systematic fashion detection rates are as high as 80 %.

·               Transabdominal and transvaginal sonography in combination increase detection of fetal anomalies in the first trimester.

·               Exencephaly–anencephaly sequence, omphalocele, gastroschisis, and holoprosencephaly are anomalies with 100 % detection rates reported in the first trimester.

References

1.

Bromley B, Shipp TD, Lyons J, Navathe RS, Groszmann Y, Benacerraf BR. Detection of fetal structural anomalies in a basic first-trimester screening program for aneuploidy. J Ultrasound Med. 2014;33(10):1737–45.CrossRefPubMed

2.

Becker R, Wegner RD. Detailed screening for fetal anomalies and cardiac defects at the 11-13-week scan. Ultrasound Obstet Gynecol. 2006;27(6):613–8.CrossRefPubMed

3.

O’Keeffe DF, Abuhamad A. Obstetric ultrasound utilization in the United States: data from various health plans. Semin Perinatol. 2013;37(5):292–4.CrossRefPubMed

4.

Timor-Tritsch IE, Monteagudo A, Peisner DB. High-frequency transvaginal sonographic examination for the potential malformation assessment of the 9-week to 14-week fetus. J Clin Ultrasound. 1992;20(4):231–8.CrossRefPubMed

5.

Whitlow BJ, Economides DL. The optimal gestational age to examine fetal anatomy and measure nuchal translucency in the first trimester. Ultrasound Obstet Gynecol. 1998;11(4):258–61.CrossRefPubMed

6.

Souka AP, Pilalis A, Kavalakis Y, Kosmas Y, Antsaklis P, Antsaklis A. Assessment of fetal anatomy at the 11-14-week ultrasound examination. Ultrasound Obstet Gynecol. 2004;24(7):730–4.CrossRefPubMed

7.

Timor-Tritsch IE, Bashiri A, Monteagudo A, Arslan AA. Qualified and trained sonographers in the US can perform early fetal anatomy scans between 11 and 14 weeks. Am J Obstet Gynecol. 2004;191(4):1247–52.CrossRefPubMed

8.

Rossi AC, Prefumo F. Accuracy of ultrasonography at 11-14 weeks of gestation for detection of fetal structural anomalies: a systematic review. Obstet Gynecol. 2013;122(6):1160–7.CrossRefPubMed

9.

American Institute of Ultrasound in M. AIUM practice guideline for the performance of obstetric ultrasound examinations. J Ultrasound Med. 2013;32(6):1083–101.CrossRef

10.

Salomon LJ, Alfirevic Z, Bilardo CM, Chalouhi GE, Ghi T, Kagan KO, et al. ISUOG practice guidelines: performance of first-trimester fetal ultrasound scan. Ultrasound Obstet Gynecol. 2013;41(1):102–13.CrossRefPubMed

11.

Copp AJ, Greene ND. Neural tube defects–disorders of neurulation and related embryonic processes. Wiley Interdiscip Rev Dev Biol. 2013;2(2):213–27.PubMedCentralCrossRefPubMed

12.

Timor-Tritsch IE, Greenebaum E, Monteagudo A, Baxi L. Exencephaly-anencephaly sequence: proof by ultrasound imaging and amniotic fluid cytology. J Matern Fetal Med. 1996;5(4):182–5.PubMed

13.

Syngelaki A, Chelemen T, Dagklis T, Allan L, Nicolaides KH. Challenges in the diagnosis of fetal non-chromosomal abnormalities at 11-13 weeks. Prenat Diagn. 2011;31(1):90–102.CrossRefPubMed

14.

Sepulveda W, Dezerega V, Be C. First-trimester sonographic diagnosis of holoprosencephaly: value of the “butterfly” sign. J Ultrasound Med. 2004;23(6):761–5. quiz 6-7.PubMed

15.

Sepulveda W, Wong AE. First trimester screening for holoprosencephaly with choroid plexus morphology (‘butterfly’ sign) and biparietal diameter. Prenat Diagn. 2013;33(13):1233–7.CrossRefPubMed

16.

Solomon BD, Gropman A, Muenke M. Holoprosencephaly overview. In: Pagon RA, Adam MP, Ardinger HH, Bird TD, Dolan CR, Fong CT, et al., editors. GeneReviews (R). Seattle, WA: University of Washington; 1993.

17.

Raam MS, Solomon BD, Muenke M. Holoprosencephaly: a guide to diagnosis and clinical management. Indian Pediatr. 2011;48(6):457–66.PubMedCentralCrossRefPubMed

18.

Timor-Tritsch IE, Monteagudo A. Scanning techniques in obstetrics and gynecology. Clin Obstet Gynecol. 1996;39(1):167–74.CrossRefPubMed

19.

Kagan KO, Staboulidou I, Syngelaki A, Cruz J, Nicolaides KH. The 11-13-week scan: diagnosis and outcome of holoprosencephaly, exomphalos and megacystis. Ultrasound Obstet Gynecol. 2010;36(1):10–4.CrossRefPubMed

20.

Timor-Tritsch IE, Monteagudo A, Santos R. Three-dimensional inversion rendering in the first- and early second-trimester fetal brain: its use in holoprosencephaly. Ultrasound Obstet Gynecol. 2008;32(6):744–50.CrossRefPubMed

21.

Clur SA, Ottenkamp J, Bilardo CM. The nuchal translucency and the fetal heart: a literature review. Prenat Diagn. 2009;29(8):739–48.CrossRefPubMed

22.

Nafziger E, Vilensky JA. The anatomy of nuchal translucency at 10-14 weeks gestation in fetuses with trisomy 21: an incredible medical mystery. Clin Anat. 2014;27(3):353–9.CrossRefPubMed

23.

Kagan KO, Avgidou K, Molina FS, Gajewska K, Nicolaides KH. Relation between increased fetal nuchal translucency thickness and chromosomal defects. Obstet Gynecol. 2006;107(1):6–10.CrossRefPubMed

24.

Makrydimas G, Sotiriadis A, Ioannidis JP. Screening performance of first-trimester nuchal translucency for major cardiac defects: a meta-analysis. Am J Obstet Gynecol. 2003;189(5):1330–5.CrossRefPubMed

25.

Sotiriadis A, Papatheodorou S, Eleftheriades M, Makrydimas G. Nuchal translucency and major congenital heart defects in fetuses with normal karyotype: a meta-analysis. Ultrasound Obstet Gynecol. 2013;42(4):383–9.PubMed

26.

Molina FS, Avgidou K, Kagan KO, Poggi S, Nicolaides KH. Cystic hygromas, nuchal edema, and nuchal translucency at 11-14 weeks of gestation. Obstet Gynecol. 2006;107(3):678–83.CrossRefPubMed

27.

Malone FD, Ball RH, Nyberg DA, Comstock CH, Saade GR, Berkowitz RL, et al. First-trimester septated cystic hygroma: prevalence, natural history, and pediatric outcome. Obstet Gynecol. 2005;106(2):288–94.CrossRefPubMed

28.

Scholl J, Durfee SM, Russell MA, Heard AJ, Iyer C, Alammari R, et al. First-trimester cystic hygroma: relationship of nuchal translucency thickness and outcomes. Obstet Gynecol. 2012;120(3):551–9.CrossRefPubMed

29.

Nicolaides KH. Screening for fetal aneuploidies at 11 to 13 weeks. Prenat Diagn. 2011;31(1):7–15.CrossRefPubMed

30.

Dukhovny S, Wilkins-Haug L, Shipp TD, Benson CB, Kaimal AJ, Reiss R. Absent fetal nasal bone: what does it mean for the euploid fetus? J Ultrasound Med. 2013;32(12):2131–4.CrossRefPubMed

31.

Mossey PA, Little J, Munger RG, Dixon MJ, Shaw WC. Cleft lip and palate. Lancet. 2009;374(9703):1773–85.CrossRefPubMed

32.

Martinez-Ten P, Adiego B, Perez-Pedregosa J, Illescas T, Wong AE, Sepulveda W. First-trimester assessment of the nasal bones using the retronasal triangle view: a 3-dimensional sonographic study. J Ultrasound Med. 2010;29(11):1555–61.PubMed

33.

Sepulveda W, Wong AE, Martinez-Ten P, Perez-Pedregosa J. Retronasal triangle: a sonographic landmark for the screening of cleft palate in the first trimester. Ultrasound Obstet Gynecol. 2010;35(1):7–13.CrossRefPubMed

34.

Adiego B, Martinez-Ten P, Illescas T, Bermejo C, Sepulveda W. First-trimester assessment of nasal bone using retronasal triangle view: a prospective study. Ultrasound Obstet Gynecol. 2014;43(3):272–6.CrossRefPubMed

35.

Leonard A, Bernard P, Hiel AL, Hubinont C. Prenatal diagnosis of fetal cataract: case report and review of the literature. Fetal Diagn Ther. 2009;26(2):61–7.CrossRefPubMed

36.

Monteagudo A, Timor-Tritsch IE, Friedman AH, Santos R. Autosomal dominant cataracts of the fetus: early detection by transvaginal ultrasound. Ultrasound Obstet Gynecol. 1996;8(2):104–8.CrossRefPubMed

37.

Paladini D. Fetal micrognathia: almost always an ominous finding. Ultrasound Obstet Gynecol. 2010;35(4):377–84.CrossRefPubMed

38.

Rotten D, Levaillant JM, Martinez H, Ducou le Pointe H, Vicaut E. The fetal mandible: a 2D and 3D sonographic approach to the diagnosis of retrognathia and micrognathia. Ultrasound Obstet Gynecol. 2002;19(2):122–30.CrossRefPubMed

39.

Bernard JP, Suarez B, Rambaud C, Muller F, Ville Y. Prenatal diagnosis of neural tube defect before 12 weeks’ gestation: direct and indirect ultrasonographic semeiology. Ultrasound Obstet Gynecol. 1997;10(6):406–9.CrossRefPubMed

40.

Baxi L, Warren W, Collins MH, Timor-Tritsch IE. Early detection of caudal regression syndrome with transvaginal scanning. Obstet Gynecol. 1990;75(3 Pt 2):486–9.PubMed

41.

Blumenfeld Z, Siegler E, Bronshtein M. The early diagnosis of neural tube defects. Prenat Diagn. 1993;13(9):863–71.CrossRefPubMed

42.

Chaoui R, Benoit B, Mitkowska-Wozniak H, Heling KS, Nicolaides KH. Assessment of intracranial translucency (IT) in the detection of spina bifida at the 11-13-week scan. Ultrasound Obstet Gynecol. 2009;34(3):249–52.CrossRefPubMed

43.

Lachmann R, Chaoui R, Moratalla J, Picciarelli G, Nicolaides KH. Posterior brain in fetuses with open spina bifida at 11 to 13 weeks. Prenat Diagn. 2011;31(1):103–6.CrossRefPubMed

44.

Garcia-Posada R, Eixarch E, Sanz M, Puerto B, Figueras F, Borrell A. Cisterna magna width at 11-13 weeks in the detection of posterior fossa anomalies. Ultrasound Obstet Gynecol. 2013;41(5):515–20.CrossRefPubMed

45.

Bernard JP, Cuckle HS, Stirnemann JJ, Salomon LJ, Ville Y. Screening for fetal spina bifida by ultrasound examination in the first trimester of pregnancy using fetal biparietal diameter. Am J Obstet Gynecol. 2012;207(4):306.e1–5.CrossRef

46.

Khalil A, Coates A, Papageorghiou A, Bhide A, Thilaganathan B. Biparietal diameter at 11-13 weeks’ gestation in fetuses with open spina bifida. Ultrasound Obstet Gynecol. 2013;42(4):409–15.PubMed

47.

Simon EG, Arthuis CJ, Haddad G, Bertrand P, Perrotin F. A biparietal/transverse abdominal diameter (BPD/TAD) ratio ≤1: a potential hint for open spina bifida at 11-13 weeks scan. Ultrasound Obstet Gynecol. 2015;45:267.CrossRefPubMed

48.

Clur SA, Bilardo CM. Early detection of fetal cardiac abnormalities: how effective is it and how should we manage these patients? Prenat Diagn. 2014;34(13):1235–45.CrossRefPubMed

49.

Chelemen T, Syngelaki A, Maiz N, Allan L, Nicolaides KH. Contribution of ductus venosus Doppler in first-trimester screening for major cardiac defects. Fetal Diagn Ther. 2011;29(2):127–34.CrossRefPubMed

50.

Pereira S, Ganapathy R, Syngelaki A, Maiz N, Nicolaides KH. Contribution of fetal tricuspid regurgitation in first-trimester screening for major cardiac defects. Obstet Gynecol. 2011;117(6):1384–91.CrossRefPubMed

51.

McHoney M. Congenital diaphragmatic hernia. Early Hum Dev. 2014;90(12):941–6.CrossRefPubMed

52.

Sebire NJ, Snijders RJ, Davenport M, Greenough A, Nicolaides KH. Fetal nuchal translucency thickness at 10-14 weeks’ gestation and congenital diaphragmatic hernia. Obstet Gynecol. 1997;90(6):943–6.CrossRefPubMed

53.

Mastroiacovo P, Lisi A, Castilla EE, Martinez-Frias ML, Bermejo E, Marengo L, et al. Gastroschisis and associated defects: an international study. Am J Med Genet Part A. 2007;143A(7):660–71.CrossRefPubMed

54.

Prefumo F, Izzi C. Fetal abdominal wall defects. Best Pract Res Clin Obstet Gynaecol. 2014;28(3):391–402.CrossRefPubMed

55.

Iacovella C, Contro E, Ghi T, Pilu G, Papageorghiou A, Thilaganathan B, et al. The effect of the contents of exomphalos and nuchal translucency at 11-14 weeks on the likelihood of associated chromosomal abnormality. Prenat Diagn. 2012;32(11):1066–70.CrossRefPubMed

56.

Khalil A, Arnaoutoglou C, Pacilli M, Szabo A, David AL, Pandya P. Outcome of fetal exomphalos diagnosed at 11-14 weeks of gestation. Ultrasound Obstet Gynecol. 2012;39(4):401–6.CrossRefPubMed

57.

Lakasing L, Cicero S, Davenport M, Patel S, Nicolaides KH. Current outcome of antenatally diagnosed exomphalos: an 11 year review. J Pediatr Surg. 2006;41(8):1403–6.CrossRefPubMed

58.

Mandrekar SR, Amoncar S, Banaulikar S, Sawant V, Pinto RG. Omphalocele, exstrophy of cloaca, imperforate anus and spinal defect (OEIS Complex) with overlapping features of body stalk anomaly (limb body wall complex). Ind J Hum Genet. 2014;20(2):195–8.CrossRef

59.

Russo R, D’Armiento M, Angrisani P, Vecchione R. Limb body wall complex: a critical review and a nosological proposal. Am J Med Genet. 1993;47(6):893–900.CrossRefPubMed

60.

Smith NM, Chambers HM, Furness ME, Haan EA. The OEIS complex (omphalocele-exstrophy-imperforate anus-spinal defects): recurrence in sibs. J Med Genet. 1992;29(10):730–2.PubMedCentralCrossRefPubMed

61.

Feldkamp ML, Botto LD, Amar E, Bakker MK, Bermejo-Sanchez E, Bianca S, et al. Cloacal exstrophy: an epidemiologic study from the International Clearinghouse for Birth Defects Surveillance and Research. Am J Med Genet C Semin Med Genet. 2011;157C(4):333–43.CrossRefPubMed

62.

Timor-Tritsch IE, Monteagudo A, Horan C, Stangel JJ. Dichorionic triplet pregnancy with the monoamniotic twin pair concordant for omphalocele and bladder exstrophy. Ultrasound Obstet Gynecol. 2000;16(7):669–71.CrossRefPubMed

63.

Tong SY, Lee JE, Kim SR, Lee SK. Umbilical cord cyst: a prenatal clue to bladder exstrophy. Prenat Diagn. 2007;27(12):1177–9.CrossRefPubMed

64.

Goyal A, Fishwick J, Hurrell R, Cervellione RM, Dickson AP. Antenatal diagnosis of bladder/cloacal exstrophy: challenges and possible solutions. J Pediatr Urol. 2012;8(2):140–4.CrossRefPubMed

65.

Gearhart JP, Ben-Chaim J, Jeffs RD, Sanders RC. Criteria for the prenatal diagnosis of classic bladder exstrophy. Obstet Gynecol. 1995;85(6):961–4.CrossRefPubMed

66.

Bischoff A, Calvo-Garcia MA, Baregamian N, Levitt MA, Lim FY, Hall J, et al. Prenatal counseling for cloaca and cloacal exstrophy-challenges faced by pediatric surgeons. Pediatr Surg Int. 2012;28(8):781–8.CrossRefPubMed

67.

Peixoto-Filho FM, do Cima LC, Nakamura-Pereira M. Prenatal diagnosis of Pentalogy of Cantrell in the first trimester: is 3-dimensional sonography needed? J Clin Ultrasound. 2009;37(2):112–4.CrossRefPubMed

68.

Platt LD. Should the first trimester ultrasound include anatomy survey? Semin Perinatol. 2013;37(5):310–22.CrossRefPubMed

69.

De Biasio P, Prefumo F, Lantieri PB, Venturini PL. Reference values for fetal limb biometry at 10-14 weeks of gestation. Ultrasound Obstet Gynecol. 2002;19(6):588–91.CrossRefPubMed

70.

Gray BL, Calfee RP, Dicke JM, Steffen J, Goldfarb CA. The utility of prenatal ultrasound as a screening tool for upper extremity congenital anomalies. J Hand Surg. 2013;38(11):2106–11.CrossRef

71.

Ermito S, Dinatale A, Carrara S, Cavaliere A, Imbruglia L, Recupero S. Prenatal diagnosis of limb abnormalities: role of fetal ultrasonography. J Prenat Med. 2009;3(2):18–22.PubMedCentralPubMed

72.

Pajkrt E, Cicero S, Griffin DR, van Maarle MC, Chitty LS. Fetal forearm anomalies: prenatal diagnosis, associations and management strategy. Prenat Diagn. 2012;32(11):1084–93.CrossRefPubMed

73.

Kshirsagar VY, Ahmed M, Colaco SM. Sirenomelia apus: a rare deformity. J Clin Neonatol. 2012;1(3):146–8.PubMedCentralCrossRefPubMed

74.

Tuuli MG, Norman SM, Odibo AO, Macones GA, Cahill AG. Perinatal outcomes in women with subchorionic hematoma: a systematic review and meta-analysis. Obstet Gynecol. 2011;117(5):1205–12.CrossRefPubMed

75.

Bennett GL, Bromley B, Lieberman E, Benacerraf BR. Subchorionic hemorrhage in first-trimester pregnancies: prediction of pregnancy outcome with sonography. Radiology. 1996;200(3):803–6.CrossRefPubMed

76.

Lamberty CO, de Carvalho MH, Miguelez J, Liao AW, Zugaib M. Ultrasound detection rate of single umbilical artery in the first trimester of pregnancy. Prenat Diagn. 2011;31(9):865–8.PubMed

77.

Martinez-Payo C, Cabezas E. Detection of single umbilical artery in the first trimester ultrasound: its value as a marker of fetal malformation. Biomed Res Int. 2014;2014:548729.PubMedCentralCrossRefPubMed

78.

Murphy-Kaulbeck L, Dodds L, Joseph KS, Van den Hof M. Single umbilical artery risk factors and pregnancy outcomes. Obstet Gynecol. 2010;116(4):843–50.CrossRefPubMed

79.

Martinez-Payo C, Gaitero A, Tamarit I, Garcia-Espantaleon M, Iglesias GE. Perinatal results following the prenatal ultrasound diagnosis of single umbilical artery. Acta Obstet Gynecol Scand. 2005;84(11):1068–74.CrossRefPubMed

80.

Budorick NE, Kelly TF, Dunn JA, Scioscia AL. The single umbilical artery in a high-risk patient population: what should be offered? J Ultrasound Med. 2001;20(6):619–27. quiz 28.PubMed

81.

Prefumo F, Guven MA, Carvalho JS. Single umbilical artery and congenital heart disease in selected and unselected populations. Ultrasound Obstet Gynecol. 2010;35(5):552–5.CrossRefPubMed

82.

Gornall AS, Kurinczuk JJ, Konje JC. Antenatal detection of a single umbilical artery: does it matter? Prenat Diagn. 2003;23(2):117–23.CrossRefPubMed

83.

Hua M, Odibo AO, Macones GA, Roehl KA, Crane JP, Cahill AG. Single umbilical artery and its associated findings. Obstet Gynecol. 2010;115(5):930–4.CrossRefPubMed

84.

Reddy UM, Abuhamad AZ, Levine D, Saade GR. Fetal Imaging Workshop Invited P. Fetal imaging: executive summary of a Joint Eunice Kennedy Shriver National Institute of Child Health and Human Development, Society for Maternal-Fetal Medicine, American Institute of Ultrasound in Medicine, American College of Obstetricians and Gynecologists, American College of Radiology, Society for Pediatric Radiology, and Society of Radiologists in Ultrasound Fetal Imaging Workshop. Am J Obstet Gynecol. 2014;210(5):387–97.CrossRefPubMed