From the Guidelines
Maternal Serum Alpha-Fetoprotein (MSAFP) is typically elevated in gastroschisis but not consistently elevated in omphalocele. In gastroschisis, MSAFP levels are markedly increased due to the direct exposure of fetal bowel to amniotic fluid through the abdominal wall defect, allowing alpha-fetoprotein to leak from the exposed intestines into the amniotic fluid and subsequently into maternal circulation 1. The key difference between gastroschisis and omphalocele lies in the presence or absence of a protective membrane covering the herniated abdominal contents.
- In gastroschisis, the absence of this membrane leads to significant leakage of alpha-fetoprotein and consequently elevated MSAFP levels.
- In omphalocele, the protective membrane covering the herniated contents prevents significant leakage of alpha-fetoprotein, resulting in normal or only mildly elevated MSAFP levels 1. Additionally, omphalocele is frequently associated with chromosomal abnormalities, which can actually result in decreased MSAFP levels, potentially counterbalancing any mild elevation. This distinction in MSAFP levels can be a helpful diagnostic clue when differentiating between these two anterior abdominal wall defects during prenatal screening, though ultrasound remains the definitive diagnostic tool. The technical standards and guidelines for prenatal screening support the notion that open ventral wall defects, such as gastroschisis, are associated with very elevated amniotic fluid AFP, whereas omphalocele can have normal to elevated amniotic fluid AFP 1.
From the Research
MSAFP Levels in Gastroschisis and Omphalocele
- MSAFP levels are elevated in both gastroschisis and omphalocele, as indicated by studies 2, 3, 4.
- A study from 1997 2 found that elevated MSAFP levels are associated with certain morphologic anomalies of the fetus, including abdominal wall defects such as omphalocele and gastroschisis.
- Another study from 1988 3 reported that elevated MS-AFP is associated with several fetal anomalies, including ventral abdominal wall defects, which include both gastroschisis and omphalocele.
- A population-based study from 1988 4 analyzed MSAFP distributions for cases of gastroschisis and omphalocele, finding that median MSAFP values were higher for gastroschisis (7.0 multiples of the median) than for omphalocele (4.1 multiples of the median).
Comparison of MSAFP Levels in Gastroschisis and Omphalocele
- The study from 1988 4 found that the MSAFP distributions for gastroschisis and omphalocele were both log-Gaussian, but the log standard deviation was smaller for gastroschisis than for omphalocele.
- A more recent study from 2024 5 found that MSAFP screening is not associated with earlier detection of omphalocele, and that the results of MSAFP screening are not predictive of clinical outcomes in pregnancies with prenatally diagnosed omphalocele.
- Another study from 1998 6 reported that omphalocele was identified in four patients, two with normal and two with elevated MSAFP, while gastroschisis was found in one patient with low MSAFP and one with elevated MSAFP.
Clinical Implications
- The studies suggest that elevated MSAFP levels are associated with an increased risk of abdominal wall defects, including both gastroschisis and omphalocele 2, 3, 4.
- However, the results of MSAFP screening should be interpreted with caution, as they may not be predictive of clinical outcomes in all cases 5, 6.
- Further evaluation, including ultrasound and amniocentesis, may be necessary to confirm the diagnosis and determine the severity of the defect 2, 3.