We retrospectively assessed the yield of early postnatal ultrasound scans in neonates with documented antenatal hydronephrosis. We reviewed recording data of prenatal renal ultrasound for 178 newborn infants and the results of renal ultrasound performed during the first days of life. Of 119 infants with prenatal diagnosis of mild hydronephrosis (renal pelvic diameter <10 mm), 116 (97.5%) had postnatal ultrasound results showing normal or mild hydronephrosis. Prenatal diagnosis of severe hydronephrosis (renal pelvic diameter >20 mm; 10 infants) was correlated with high incidence (90%) of moderate and severe postnatal hydronephrosis. Prenatal diagnosis of moderate hydronephrosis (renal pelvic diameter 10 to 20 mm) resulted in moderate postnatal hydronephrosis in 20% and improvement in 80% of the newborn infants. Our evidence supports the option of delaying postnatal renal ultrasound in infants with prenatal diagnosis of mild hydronephrosis (renal pelvic diameter <10 mm). This strategy can safely reduce the number of early postnatal studies and consequently significantly decrease hospitals' inpatient workload.
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