When ultrasonography reveals a fetal abdominal wall defect
Although these fetal defects are rare, be alert to their potential presence when early ultrasonography indicates structural abnormalities. Here, surveillance, planning, and appropriate patient counseling are reviewed.
Omphalocele often is associated with abnormal karyotype
Also known as exomphalos, omphalocele is a relatively common defect, with an estimated prevalence of 2 to 3 cases per 10,000 live births.2 In this condition, there is a midline defect in which intra-abdominal contents herniate through the base of the umbilical cord. Omphaloceles are covered by amniotic membranes, making them distinguishable from gastroschisis, which has no covering, and congenital umbilical hernias, which are covered by intact skin and subcutaneous tissue.26-33
Additionally, in omphalocele the umbilical cord insertion site varies, whereas in gastroschisis the umbilical cord insertion is usually to the right of midline. An omphalocele is often categorized based on whether or not it contains the liver (extracorporeal liver) or only the bowel (intracorporeal liver).
Genetic studies
Approximately 67% to 88% of all pregnancies with omphalocele have an abnormal karyotype and/or associated malformations, including Beckwith-Wiedemann syndrome.31 Of the aneuploidies, trisomy 18 is the one most commonly associated with omphalocele, accounting for approximately 62% to 75%, while trisomy 13 accounts for approximately 11% to 24%.32,33 The presence of other anomalies is strongly associated with poor prognosis, and increased defect size is an independent predictor of neonatal morbidity and mortality, as neonates with large omphaloceles with extracorporeal livers can develop respiratory insufficiency and require more complex surgical repairs. It is interesting, however, that the absence of an extracorporeal liver is associated with a higher risk of aneuploidy than are cases with an intracorporeal liver.33
We offer chorionic villus sampling or amniocentesis to all patients with omphalocele. If the patient undergoes invasive diagnostic testing, the sample then undergoes karyotyping, chromosomal microarray, and testing for Beckwith-Wiedemann syndrome. If the patient declines diagnostic sampling, we perform a cell-free DNA screening to rule out aneuploidy.
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