An omphalocele is a ventral wall defect at the umbilicus through which abdominal contents herniate into the base of the umbilical cord. The herniated contents are contained by a peritoneal membrane, and the vessels of the umbilical cord travel through the omphalocele. Omphaloceles are associated with other anomalies in approximately 80% of cases and with aneuploidy in approximately one-half of cases. The risk of aneuploidy is lower if the omphalocele contains liver than when liver is not herniated. Omphalocele is also a component of Beckwith–Wiedemann syndrome, which also includes macroglossia (large tongue) and macrosomia (large size).

An omphalocele appears as a rounded, well-circumscribed mass protruding from the anterior abdomen at the umbilical cord insertion (Figure 13.1.1). The omphalocele sac usually
contains bowel and may also contain liver (Figure 13.1.2). Rarely, other intra-abdominal organs are herniated into the sac. The vessels of the umbilical cord travel through the omphalocele and are best imaged with color Doppler (Figure 13.1.3). Because of the association with other anomalies, a careful fetal survey should be performed after an omphalocele has been identified.

Gastroschisis is a paraumbilical defect in the anterior abdominal wall through which intra-abdominal contents, usually bowel, herniate into the amniotic cavity. Unlike an omphalocele, the herniated tissue is free-floating in the amniotic fluid, not contained by a peritoneal membrane. The defect is usually to the right of the umbilicus. Gastroschisis tends to affect young mothers more often than older mothers. Aneuploidy is uncommon. Other anomalies are present in approximately 25% of cases, many of which are related to the gastrointestinal tract, such as malrotation.