Objectives: This study was performed to analyze the predictive factors of a contralateral operation after initial pyeloplasty in patients with antenatally detected bilateral ureteropelvic junction obstruction. Methods: Patients with prenatally diagnosed bilateral ureteropelvic junction obstruction who underwent initial pyeloplasty (aged <12 months at initial pyeloplasty) were offered to participate in the study. Patients were recruited from January 2012 to December 2015. The anteroposterior renal pelvic diameter, parenchymal thickness, and calyceal dilatation were evaluated. Predictive factors of contralateral pyeloplasty after initial unilateral pyeloplasty were also examined. Results: In total, 82 patients were included in the study (mean age, 2.8 months). Among all patients who underwent initial pyeloplasty, additional contralateral pyeloplasty was required in 11 patients (13.4%). The outcome of contralateral hydronephrosis was assessed as resolution, persistence, or surgery. The median anteroposterior renal pelvic diameter and calyceal dilatation were significantly different among the groups (p < 0.001). Calyceal dilatation of ≥10 mm and a calyceal dilatation/parenchymal thickness ratio of ≥5 strongly suggested the likelihood of a contralateral operation. Conclusions: In most patients with bilateral ureteropelvic junction obstruction, improvement or resolution of contralateral hydronephrosis following initial unilateral pyeloplasty can be expected. Patients with contralateral calyceal dilatation >10 mm and the calyceal dilatation/parenchymal thickness ratio >5 are at higher risk of surgery.

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The improvement in DRF after pyeloplasty was significant for patients with an initial DRF from 30 to ≤35%. However, patients with an initial DRF from 35 to ≤40% had a greater probability of achieving normal renal function. Patients with severely impaired initial renal function had a marginal probability of achieving a normal value.