A 32-year-old pregnant woman at 30 weeks of gestation comes to her physician because of excess weight gain in a 2-week period. Ultrasonography reveals polyhydram- nios. Which fetal abnormality is most likely responsible for the polyhydramnios?

E. Polyhydramnios is associated with the inability of the fetus to swallow because of esophageal atresia or anencephaly. Polyhydramnios can also result from absorption defects such as duodenal atresia. The inability of the embryo to swallow the amniotic fluid means that the fluid cannot be absorbed into the fetal blood and removed by the placenta and passed into the maternal blood.