A 36-year-old woman comes to the clinic for ultrasonography after an elevated alpha-fetoprotein level was found during a second-trimester quadruple screen. She has had routine prenatal care since 8 weeks gestation. The patient has been taking a daily prenatal multivitamin since the first trimester and takes no other medications. She has had 2 prior spontaneous abortions but has no chronic medical conditions. The patient does not use tobacco, alcohol, or recreational drugs. Transabdominal ultrasonography reveals a fetus with thickened intestinal loops that are floating freely in the amniotic sac. There is also decreased fluid in the amniotic sac, suggestive of oligohydramnios. This patient's ultrasonographic finding is most likely due to which of the following conditions?
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This fetus has free-floating intestinal loops within the amniotic sac, findings diagnostic of gastroschisis, a full-thickness abdominal wall defect lateral to the umbilicus. Herniation of uncovered bowel allows alpha-fetoprotein (AFP) to pass through the exposed bowel into the amniotic fluid, resulting in elevated maternal serum AFP.
Gastroschisis is usually an isolated defect without associated extraintestinal anomalies. However, fetal growth restriction is common due to nutrient loss across the exposed bowel. Blood and nutrients are then shunted away from the kidneys to vital organs (eg, brain), resulting in decreased fetal urine production and oligohydramnios (reduced amniotic fluid), as seen in this fetus. Continued exposure of the intestines to amniotic fluid can cause chronic inflammation and edema, resulting in intestinal thickening and reduced bowel motility. In some cases, this may ultimately lead to bowel obstruction, resulting in polyhydramnios instead.
After delivery, the lower half of the infant is placed in a sterile plastic bag to minimize insensible heat and fluid losses, and a nasogastric or orogastric tube is placed to decompress the stomach. Definitive management is surgical repair.
(Choice A) Beckwith-Wiedemann syndrome is associated with omphalocele. In contrast to gastroschisis, omphalocele is a midline abdominal wall defect in which the herniated abdominal contents are contained within a membranous sac.
(Choice B) Infants with cystic fibrosis are at risk for meconium ileus, an intestinal obstruction due to inspissated meconium. Prenatal ultrasonography may reveal thickened, dilated intestinal loops; however, the abdominal wall is intact and the intestines are not free floating.
(Choice D) Prune belly syndrome is due to a defect in abdominal musculature. Intestinal loops may be seen through the thin abdominal wall, causing the prune appearance, but are covered by skin (not free floating).
(Choice E) Trisomy 21 is associated with umbilical hernia (abdominal wall defect covered by skin) and duodenal atresia, which is characterized by a "double bubble" and polyhydramnios on ultrasonography. In addition, AFP is reduced (not elevated) in trisomy 21.
Educational objective:
Gastroschisis is a full-thickness abdominal wall defect with herniation of uncovered bowel; it is usually an isolated condition. Passing of alpha-fetoprotein across exposed bowel results in elevated maternal levels, and prenatal ultrasonography shows free-floating intestinal loops.