Antenatal and Postnatal Ultrasound Factors Associated with Surgical Intervention in Antenatally Diagnosed Hydronephrosis

Background: Predicting the need for surgical intervention in infants with antenatally diagnosed hydronephrosis (ANH) remains challenging. This study aimed to identify antenatal and postnatal factors associated with surgical intervention in infants with ANH. Method: This prospective observational study included infants aged less than 6 months with antenatally diagnosed hydronephrosis. Antenatal Society for Fetal Urology (SFU) and anterior–posterior pelvic diameter (APD) grades were obtained from maternal antenatal ultrasound reports, and the infants were followed for 6 months after birth. Demographic characteristics and antenatal and postnatal radiological findings were compared between infants who underwent surgical intervention and those managed conservatively. SFU and APD grades were also compared according to postnatal outcomes. In addition, the association of postnatal APD with surgical intervention was evaluated, and an exploratory cutoff value was determined. Result: Among 53 infants with antenatally diagnosed hydronephrosis, 18 had bilateral hydronephrosis, yielding a total of 71 renal units for renal-unit level analyses, 16 (22.5%) required surgery. Infants undergoing surgery had reduced renal parenchymal thickness, higher SFU grades (III/IV), greater postnatal APD (29.5 vs. 7.8 mm; p ≤ 0.001), and less preserved corticomedullary differentiation (31.2% vs. 92.7%; p < 0.001). Higher APD grade (OR 6.3, 95% CI 1.9–26.5; p = 0.001), SFU grade (OR 6.64, 95% CI 2.1–21.0; p = 0.001), and postnatal APD (OR 1.16, 95% CI 1.06–1.29; p = 0.004) were independently associated with surgical intervention. A postnatal APD cutoff of 13 mm showed good diagnostic accuracy (AUC = 0.87 (95% CI 0.77–0.96), p = 0.001). Conclusion: Antenatal SFU grade and APD grade and postnatal APD were strongly associated with subsequent surgical intervention and represented key factors influencing surgical decision-making during follow-up.