Diagnosis and fetal development
Prior to widespread use of routine early fetal ultrasound assessment, abnormal MSAFP was often the first indication that a birth defect might be present. Elevated MSAFP is seen in virtually all cases of fetal gastroschisis and can be fairly high with median MSAFP multiples of the median (MoMs) from 7.0–9.4 MoMs, which are higher than seen with fetal omphalocele (median MSAFP 4.2 MoMs).13
Most cases of gastroschisis are diagnosed by ultrasound. Correct identification of gastroschisis has improved as technological advances have improved the clarity of ultrasound images and interpretation skills have developed. Older population studies show detection rates of approximately 85%, while newer population studies show rates of approximately 97.5%.4,14
Transabdominal ultrasound assessment reveals loops of fetal bowel in the amniotic cavity which are free-floating and not covered by a membrane. Closer examination of the umbilical cord insertion reveals a normally inserted umbilical cord with a small abdominal wall defect virtually always located to the right of the cord insertion. In contrast, omphalocele presents as a smooth, rounded mass containing abdominal contents. The mass is centrally located at the level of the umbilical cord insertion disrupting the normal cord insertion anatomy and the umbilical vessels can be seen coursing across the surface of the mass. Often, gastroschisis is described as having a cauliflower-like appearance, due to the presence of amniotic fluid between bowel loops creating acoustic interfaces at near and fall bowel walls.
Gastroschisis may be seen on ultrasound after resolution of physiologic gut herniation by 12 weeks’ gestation.9 The main differential diagnosis at that time includes other abdominal wall defects (omphalocele, ectopia cordis, Pentalogy of Cantrell), amniotic bands and body stalk abnormalities, bladder extrophy, and umbilical cord cysts. Due to the association between fetal anomalies (structural and chromosomal) and omphalocele, early differentiation between omphalocele and gastroschisis is critical to provide correct antepartum counseling to a patient. Although risk of additional birth defects and chromosomal abnormalities is low, associated gastrointestinal abnormalities are more common in gastroschisis.
Amniotic fluid is an irritant to the sensitive intestinal tissue and prolonged exposure of the bowel to amniotic fluid induces inflammation, bowel wall edema, and abnormal motility (hypoperistalsis). In fact, extra-abdominal bowel dilation (defined as diameter greater than 10 mm) is a common finding in gastroschisis, and since the 1980s, dilation of extra-abdominal bowel has been examined as a marker for possible poor postnatal prognosis. A retrospective review of 191 cases of gastroschisis revealed that 45% had extra-abdominal bowel dilation, but no association with adverse neonatal outcome.15 In addition, a systematic review of 10 observational studies concluded that fetuses with isolated gastroschisis and extra-abdominal bowel dilation are not at increased risk of adverse perinatal outcome compared with fetuses without dilation.16 Due to the current lack of association between antenatal appearance of extra-abdominal bowel and neonatal outcome, delivery planning should not be based on prenatal assessment of extra-abdominal fetal bowel.
While extra-abdominal bowel dilation is common and does not appear to be significantly associated with postnatal prognosis, it is important to note that there is a significant association between gastroschisis and other gastrointestinal abnormalities. A systematic review and analysis found a 17% risk of gastrointestinal complications including atresia, stenosis volvulus, perforation, or necrosis.17,18 In utero bowel obstruction (mechanical or anatomical) may be suspected when progressive intraabdominal dilation of the stomach and intestines is appreciated. Polyhydramnios may serve as a marker for intestinal obstruction and be a risk factor for a more complicated postnatal course.19 The presence of additional gastrointestinal abnormalities can affect the postnatal course by increasing neonatal morbidity and mortality and prolonging postnatal recovery.18