Accuracy of prenatal ultrasonographic diagnosis of duplex renal system.

Duplex renal system is a rare congenital anomaly of the urinary tract that can be diagnosed in utero. The purpose of this study was to establish the optimal diagnostic criteria for fetal renal duplication in a population undergoing prenatal sonographic screening. Between January 1989 and June 1997 we found 11 cases of duplex renal system, 10 of which were correctly identified in utero at a median gestational age of 28 weeks (range, 20 to 38 weeks), and one of which was a false-negative diagnosis. Prenatal diagnosis of duplex renal system can be made in utero during the second half of pregnancy in the presence of two or more of the following signs: hydronephrosis limited to one pole in a kidney with two separate, noncommunicating renal pelves; ipsilateral megaureter; and ureterocele.