What characteristic defines omphalocele as opposed to gastroschisis?

Omphalocele is characterized by the presence of abdominal contents that are covered by a membrane, specifically involving a hernia sac that protrudes through the umbilical ring. This condition is often associated with various chromosomal abnormalities, including trisomy 21. The presence of congenital anomalies in cases of omphalocele, such as cardiac defects and other syndromic features, supports this association.

In contrast, gastroschisis presents with the intestines protruding through a defect in the abdominal wall to the right of the umbilicus and typically does not have a hernia sac. Gastroschisis is generally not associated with chromosomal abnormalities and occurs more often as an isolated condition. Therefore, while the other options provide different definitions or associations, it is the link to trisomy 21 that distinctly aligns omphalocele with a genetic syndrome, setting it apart from gastroschisis.