Reversal of acute polyhydramnios after fetal renal decompression

Polyhydramnios and premature labor at twenty-seven weeks secondary to an intrafetal renal cyst are described. Antenatal fetal cyst decompression successfully reversed the polyhydramnios and prevented premature delivery, resulting in a full-term healthy infant delivered vaginally at thirty-nine weeks. Urologic investigation postpartum revealed a probable congenital ureteropelvic junction obstruction.