Which factor is the most important predictor of long-term renal function in newborns with prenatal hydronephrosis?

• A. Oligohydramnios
• B. Anteroposterior diameter measurement of 5-15 mm by prenatal ultrasound
• C. Polyhydramnios
• D. Normal amniotic fluid

Answer: (A)

Oligohydramnios best predicts long-term renal function because fetal urine output largely determines amniotic fluid volume. When amniotic fluid is low, it signals the kidneys are not producing enough urine, reflecting reduced renal function or severe urinary tract obstruction. This reduced output in utero is strongly linked to poorer renal development and higher risk of postnatal renal impairment, making oligohydramnios the strongest indicator of future renal prognosis in newborns with prenatal hydronephrosis.

In contrast, the ultrasound measurement of how dilated the renal pelvis appears shows severity of hydronephrosis but does not reliably determine final kidney function. Polyhydramnios or normal amniotic fluid levels are less directly predictive of renal outcome in this context, as they don’t specifically indicate compromised fetal kidney function.