Omphalocele and Gastroschisis fall under an umbrella of ventral/anterior thoraco-abdominal wall defects that also include bladder extrophy and ectopia cordis.
Prenatal ultrasound is essential in the detection of these conditions.
Fetal gut herniation is a normal part of intrauterine development. Begins at 6-8 weeks and completes by 10-12 weeks.
The gut elongates or grows at a rate a rate that suprasses the growth rate of the abdomen leading to gut herniation into the base of the umbilical cord. The bowel then rotates 90 degrees counter-clockwise (from our perspective) around a superior mesentery artery axis, establishing the anatomical position of the large intestine within the abdominal cavity. This herniation not measure more than 0.7 cm or be seen in when the CRL is longer than 4.4 cm
Omphalocele
Fetal gut, liver or other abdominal organ herniating into the umbilical cord. Covered by peritoneum.
Associated with elevated alpha-fetoprotein
Advanced maternal age
Other congenital anomalies ~ 30%
Trisomies 13, 18 and 21
Gastroschisis
Herniation of gut through an abdominal wall defect, not covered in peritneum. The bowel is in direct contact with amniotic fluid.
Not associated with umbilical cord, it is not a midline lesion.
Associated with increased alpha-fetoprotein (greater than omphalocele due to intestinal contact with amniotic fluid)
Not as associated with congenital anomalies as omphalocele.
Teenage maternal age
Alcohol and Nicotine abuse
IUGR
Henry Suarez RDMS, RVT
Sources:
GI Tract Embryological Development
Embryonic development of the ventral body wall and its congenital malformations.
eMedicine: Pediatric Omphalocele and Gastroschisis
Sonographic Tendencies 