Results of systematic screening for minor degrees of fetal renal pelvis dilatation in an unselected population.

The purpose of this study was to determine the incidence of minor degrees of renal pelvis dilatation that is detected by antenatal ultrasound scanning in an unselected population and its value in the prediction of significant uropathies. This prospective study was conducted over a 24-month period. Infants with an anteroposterior pelvic diameter of >or=4 mm in the second trimester and/or >or=7 mm but <15 mm in the third trimester were enrolled. Pyelectasis was found in 4.5% of 5643 fetuses (1.5% with significant uropathy). Among the 213 infants whose cases were followed, 132 infants (62%) had renal anomalies, but only 83 infants (39%) had significant uropathies. The ability of the third-trimester renal pelvis dilatation to predict renal abnormalities showed a positive predictive value of 69%. Pyelectasis that was detected only in the second trimester revealed a significant uropathy in 12% of the infants. Pyelectasis was found in 4.5% of fetuses. The third-trimester anteroposterior renal pelvis diameter of >or=7 mm was the best ultrasound criterion to predict postnatal uropathies.