Fetal hydronephrosis: natural history and risk factors for postnatal surgery

Background: The objective of this study was to assess the ability of prenatal ultrasound to predict an unfavorable outcome and the need for postnatal surgery in cases of fetal hydronephrosis (HY). Methods: Antenatal HY was classified according to the renal pelvis anteroposterior (AP) diameter in the third trimester. Postnatal outcome was considered favorable in the presence of spontaneous resolution or postnatal diagnosis of HY < 20 mm, and unfavorable in the presence of postnatal diagnosis of > 20 mm HY or urinary tract pathologies. Results: Prenatal diagnosis of HY was made in 120 fetuses (for a total of 161 abnormal renal units). The rates of postnatal urinary tract pathology were 14, 27 and 53% for antenatal HY of = 7, 8-15 and > 15 mm, respectively. An AP diameter = 7 mm in the third trimester had a sensitivity of 100% and a specificity of 23% to predict unfavorable outcome. A formula inclusive of AP diameter and presence or absence of urinary tract anomalies can predict the need for postnatal surgery. Conclusions: The majority of infants with congenital HY have a favorable postnatal outcome. Risk of unfavorable outcome increases with the degree of dilatation of the renal pelvis and the presence of urinary tract anomalies. An AP diameter ≥ 7 mm in the third trimester warrants postnatal follow-up.