Fetal exomphalos at 11 to 14 weeks of gestation.

In an ultrasonographic screening study at 11 to 14 weeks' gestation involving 9885 singleton pregnancies, the prevalence of exomphalos was 0.11% (11 cases) and the prevalence of trisomy 18 or 13 was 0.35% (35 cases). The mean maternal age of the screened population was 35 years (range, 15 to 47 years) and a significant association was found between maternal age and both the prevalence of trisomies and the prevalence of exomphalos. Because the frequency of exomphalos in fetuses with trisomy 18 or 13 was 17% and in those with no evidence of these trisomies it was 0.05%, the risk for trisomies in fetuses with exomphalos is 340 times higher than in those without exomphalos.