An ultrasound at 26 weeks shows severe oligohydramnios with anhydramnios in a fetus later found to have bilateral multicystic dysplastic kidneys. The physiological explanation for the reduced liquor volume is loss of which contribution to amniotic fluid dynamics?
- A Transudation of fluid across the chorionic plate vessels
- B Secretion by the amniotic epithelium via aquaporin channels
- C Fetal urination, the dominant source of amniotic fluid in the second half of gestation ✓
- D Pulmonary fluid effluxing from the trachea during fetal breathing
Correct answer: C. Fetal urination, the dominant source of amniotic fluid in the second half of gestation
Explanation
From mid-gestation onward, fetal urine becomes the major source of amniotic fluid, contributing several hundred milliliters per day near term. Bilateral renal agenesis or dysplasia abolishes this input while fetal swallowing continues, producing severe oligohydramnios and the Potter sequence. Transudation and amniotic secretion matter mainly in early pregnancy, and tracheal efflux actually adds fluid, so none of these explains the finding here.
Reference: Williams Obstetrics, 25th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.