FIGURE 10-34 M-mode. In this image, there is normal concordance between atrial (A) and ventricular contractions (). Movement of the tricuspid valve en is also shown. There is also a premature atrial contraction (arrow) and a subsequent early ventricular contraction, followed by a compensatory pause.
pause that follows the premature contraction.
P ACs sometimes occur with an atrial septal aneurysm but are not associated with major structural cardiac abnormalities. Older case reports describe an association with maternal cafeine consumption and with hydralazine (Lodeiro, 1989; Oei, 1989). In approximately 2 percent of cases, afected fetuses are later identified to have a supraventricular tachycardia (S) that requires urgent treatment (Copel, 2000). Accordingly, pregnancies with fetal PACs are often followed with fetal heart rate assessment as often as every 1 to 2 weeks until ectopy resolves. T reatment of fetal SVT and other arrhythmias is discussed in Chapter 16 (p. 316) .
he integrity of the abdominal wall is assessed at the level of the cord insertion during the standard examination (Fig. 10-35).
Ventral wall defects include gastroschisis, omphalocele, and body stalk anomaly.
Gastroschisis is a full-thickness abdominal wall defect located to the right of the umbilical cord insertion. Bowel herniates through the defect into the amnionic cavity (Fig. 10-36). he prevalence is approximately 1 in 2000 births Oones, 2016; Nelson, 2015). Gastroschisis is the one major anomaly more common in fetuses of younger mothers, and the average maternal age is 20 years (Santiago-Munoz, 2007). Coexisting bowel abnormalities such as jjunal atresia are found in approximately 15 percent of cases (Nelson, 2015; Overcash, 2014). Gastroschisis is not associated with aneuploidy, and the survival rate is 90 to 95 percent (Kitchanan, 2000; Nelson, 2015; Nembhard, 2001).
Fetal-growth restriction complicates gastroschisis in 15 to 40 percent of cases (Overcash, 2014; Santiago-Munoz, 2007). Growth restriction does not appear to be associated with adverse outcomes such as longer hospitalization or higher mortality rate (Nelson, 2015; Overcash, 2014). However, earlier gestational age at delivery does pose a risk for adverse outcome with gastroschisis, and planned delivery at 36 to 37 weeks does not confer neonatal benefit (Al-Kaf, 2016; Overcash, 2014; South, 2013).
Omphalocele complicates 1 in 3000 to 5000 pregnancies (Canield, 2006; Dolk, 2010). It forms when the lateral ectomesodermal folds fail to meet in the midline. This leaves the abdominal contents covered only by a two-layered sac of amnion and peritoneum into which the umbilical cord inserts (Fig. 10-37). More than half of cases are associated with other major anomalies or aneuploidy. Omphalocele also is a component of syndromes such as Beckwith-Wiedemann, cloacal exstrophy, and pentaloy of Cantrell. Smaller defects confer greater risk for aneuploidy (De Veciana, 1994). Chromosomal microarray analysis should be ofered in all cases of omphalocele.
FIGURE 10-35 Normal ventral wall. Transverse view of the abdomen in a second-trimester fetus with an intact anterior abdominal wall and normal cord insertion.