Question 200

Question:

A 24-year-old woman has a marked increase in the size of her uterus between 26 and 30 weeks’ gestation. Ultrasonography shows a marked increase in the amount of amniotic fluid; the fetus is normal in size for gestational age. Which of the following is the most likely diagnosis?

Correct Answer: B.  Duodenal atresia

Fetal swallowing reduces the amount of amniotic fluid. Congenital gastrointestinal obstructions, such as duodenal atresia (Answer B) cause a buildup of amniotic fluid, or polyhydramnios. Erythroblastosis fetalis (Answer C) occurs when maternal and fetal blood mix, leading to alloimmune hemolysis, usually against Rh antigen. In late pregnancy, most amniotic fluid is composed of fetal urine. Renal anomalies that reduce the amount of urine production, such as horseshoe kidney (Answer D), are associated with oligohydramnios. Congenital heart disease does not manifest until after birth (Answer A). Neural tube defects (Answer E) usually do not affect the amount of amniotic fluid.