Outcome after antenatal diagnosis of upper urinary tract dilatation by ultrasonography.

A prospective study was carried out during 1986 to find out the incidence of fetal renal tract anomalies in 3228 pregnant mothers delivered in one hospital. Ultrasound examination of the fetus was performed as part of the routine antenatal assessment at 16-20 weeks' gestation, and later examinations were done if there were obstetric indications. Fetuses with any degree of dilatation of the renal pelvis or other renal tract anomalies were followed up with serial ultrasound examinations in utero and then postnatally at 6 days and 6 weeks of age, or earlier if indicated. No renal tract anomalies were detected before 28 weeks' gestation, but of 761 fetuses examined later, 62 had dilatation of the renal pelvis not associated with overdistended bladders, and one fetus was anephric. After birth 10 of these infants (16%) were found to have pronounced renal tract abnormalities. Three who had associated serious congenital abnormalities died, five infants had obstruction of the pelviureteric junction, and two infants had vesicoureteric reflux. Antenatal ultrasonographic examination after 28 weeks identifed pronounced renal tract abnormalities in asymptomatic infants with a frequency of 9.2/1000 births (seven of 761) thus permitting early treatment and reducing the incidence of late complications.