Fetal Abdominal Wall Defects Gastroschisis and Omphalocele
On this page
Direct answer
Gastroschisis is a full-thickness defect, usually to the right of the umbilicus, through which bowel herniates without any covering membrane, and it is usually isolated with a normal karyotype. Omphalocele is a midline defect at the umbilical ring in which liver and bowel sit inside a membranous sac, and it is strongly linked to aneuploidy and other malformations. Both can raise maternal serum AFP, so ultrasound is what separates them.
What you must remember
- Position: gastroschisis lies lateral to the umbilicus, usually on the right; omphalocele lies in the midline at the umbilical ring.
- Covering: gastroschisis has no membrane, so bowel loops float free in the liquor; omphalocele is covered by amnion and peritoneum, with Wharton's jelly between them.
- Contents: gastroschisis herniates small bowel; omphalocele may contain liver, which signals a larger defect.
- Karyotype: gastroschisis is usually isolated; omphalocele is strongly associated with trisomy 13, trisomy 18, Turner syndrome and Beckwith-Wiedemann syndrome.
- Biochemistry: maternal serum AFP is raised in both (more consistently in gastroschisis), so a raised AFP alone does not tell them apart.
- Associations: gastroschisis with intestinal atresia, growth restriction and young maternal age; omphalocele with cardiac defects, which need a detailed fetal echocardiogram.
Gastroschisis and omphalocele side by side
Both defects appear on the anomaly scan, and the sac, its site and the contents decide the label. The label then sets the work-up and the delivery plan, so it is worth getting right at the first scan.
| Feature | Gastroschisis | Omphalocele |
|---|---|---|
| Site | Lateral to the umbilicus, usually right | Midline at the umbilical ring |
| Covering | No membrane | Membranous sac |
| Herniated organs | Small bowel, sometimes stomach | Bowel, often liver |
| Karyotype | Usually normal | Frequently abnormal |
| Other anomalies | Intestinal atresia, growth restriction | Cardiac, neural and chromosomal |
| Ultrasound clue | Free-floating loops in the liquor | Sac at the cord insertion |
| Delivery planning | Vaginal delivery often acceptable | Caesarean often considered for a large sac with liver |
A free-floating loop of bowel beside the cord points to gastroschisis, and a membrane-covered sac at the cord insertion points to omphalocele. Once the label is set, the karyotype and cardiac scan follow from it, not from the AFP result. Neonatal repair also differs, with gastroschisis often closed primarily or through a silo, and omphalocele often needing staged closure.
Where the exam tries to catch you
Vignettes describe a fetal abdominal wall defect and then test a few predictable confusions.
- Trap: calling every abdominal wall defect an omphalocele. Correct: gastroschisis is lateral and sac-less, and it is usually isolated with a normal karyotype.
- Trap: taking a raised AFP as proof of gastroschisis. Correct: AFP rises in both defects, so the sac, its site and the contents decide the diagnosis.
- Trap: assuming a normal karyotype closes the file on an omphalocele. Correct: omphalocele needs karyotype and a detailed cardiac scan, because aneuploidy and cardiac defects are common.
- Trap: recommending caesarean for every gastroschisis. Correct: vaginal delivery is usually acceptable, with caesarean reserved for obstetric indications.
Frequently asked questions
Which abdominal wall defect is strongly linked to aneuploidy?
Omphalocele is the abdominal wall defect strongly linked to aneuploidy, especially trisomy 13, trisomy 18 and Turner syndrome. Gastroschisis is usually isolated and is most often associated with a normal karyotype.
How does gastroschisis look on ultrasound compared with omphalocele?
Gastroschisis shows bowel loops floating free in the amniotic fluid beside the umbilicus, with no covering membrane. Omphalocele shows a membrane-covered sac at the umbilical insertion that may contain liver as well as bowel.
Is caesarean section mandatory in gastroschisis?
Caesarean section is not mandatory in gastroschisis, and vaginal delivery is usually acceptable when the fetus is otherwise well. Caesarean is reserved for obstetric indications, and delivery is planned at a tertiary centre with paediatric surgery available.
Why is maternal AFP raised in abdominal wall defects?
Maternal serum AFP rises when fetal serum AFP leaks into the maternal circulation, most consistently and highly through the exposed bowel of gastroschisis and less consistently in omphalocele. It cannot separate gastroschisis from omphalocele, so ultrasound and karyotype are needed to confirm the diagnosis.
Which syndrome links omphalocele with macroglossia?
Beckwith-Wiedemann syndrome links omphalocele with macroglossia, somatic overgrowth and neonatal hypoglycaemia. A newborn with an omphalocele should therefore be screened for that syndrome and for hypoglycaemia.