Which condition leads to marked oligohydramnios due to decreased fetal urine output?

Which condition leads to marked oligohydramnios due to decreased fetal urine output?

• A. Renal agenesis
• B. Polyhydramnios due to GI obstruction
• C. Maternal diabetes with polyuria
• D. Chronic hypertension

Answer: (A)

Amniotic fluid largely comes from fetal urine once fetal kidneys are functioning, so when urine production drops, fluid volume falls. Bilateral renal agenesis means the fetus fails to develop kidneys, producing little or no urine; this directly causes marked oligohydramnios because there is essentially no fetal urine to contribute to the amniotic fluid. The other scenarios don’t fit this mechanism: a GI obstruction leads to polyhydramnios because the fetus can’t swallow fluid, causing excess fluid; maternal diabetes with polyuria tends to cause fetal polyhydramnios due to increased fetal urine production; chronic hypertension can be associated with oligohydramnios through placental insufficiency affecting overall fetal well-being, but the classic, direct cause of marked oligohydramnios via decreased fetal urine output is absent kidneys from renal agenesis.

Amniotic fluid largely comes from fetal urine once fetal kidneys are functioning, so when urine production drops, fluid volume falls. Bilateral renal agenesis means the fetus fails to develop kidneys, producing little or no urine; this directly causes marked oligohydramnios because there is essentially no fetal urine to contribute to the amniotic fluid. The other scenarios don’t fit this mechanism: a GI obstruction leads to polyhydramnios because the fetus can’t swallow fluid, causing excess fluid; maternal diabetes with polyuria tends to cause fetal polyhydramnios due to increased fetal urine production; chronic hypertension can be associated with oligohydramnios through placental insufficiency affecting overall fetal well-being, but the classic, direct cause of marked oligohydramnios via decreased fetal urine output is absent kidneys from renal agenesis.