Polyhydramnios is frequently observed in all of the following conditions except:

D. Hirschsprung's disease.

DISCUSSION: Polyhydramnios is defined as excessive amounts of fluid (>2000 ml.) in the amniotic sac during pregnancy. The amniotic pool is a dynamic pool with a relatively rapid turnover. In the fourth intrauterine month the fetus begins to swallow amniotic fluid (25% to 40% of the volume) and absorbs the fluid from the upper gastrointestinal tract. The fluid is urinated back out into the amniotic pool by the fetal kidneys and a functioning bladder. Although there are maternal causes of polyhydramnios (cardiac failure, renal failure, other causes of fluid retention) and some idiopathic cases, many instances are related to the presence of fetal anomalies. These include central nervous system problems such as anencephaly, which prevents normal swallowing, and any high alimentary tract obstruction that blocks the passage of the amniotic fluid and prevents its absorption (including esophageal atresia, pyloric atresia, and duodenal atresia). In addition, infants with congenital diaphragmatic hernia have obstructions due to herniation of the stomach and bowel into the thoracic cavity. This is a poor prognostic finding in these infants. Hirschsprung's disease is a form of low intestinal obstruction, and therefore an adequate length of proximal patent intestine is available for absorption of the swallowed amniotic fluid and polyhydramnios is usually not present.