Antenatal diagnosis of urinary tract abnormalities by ultrasonography after 28 weeks' gestation: incidence and outcome.

Objective: The objective was to establish the likelihood that antenatal upper urinary tract dilatation identified after 28 weeks of gestation will progress to significant postnatal uropathy.

Methods: In 5 years, 3856 fetuses had ultrasonography after 28 weeks of gestation when the mothers were first seen in advanced pregnancy for delivery appointments or for other obstetric indications. Fetuses with urinary tract anomalies had ultrasonographic surveillance after 6 days and 6 weeks of life with further evaluation as necessary.

Results: Renal tract anomalies were identified in 313 fetuses, and 55 infants had significant renal tract abnormalities. There were 7 deaths; 2 infants were anephric and 5 with hydronephrosis had lethal congenital abnormalities. Dilatation of the upper urinary tract was identified in 7.7% of the fetuses (298/3856) but was transient in 216 of them (72%). Follow-up of children with transient renal pelvis dilatation found only one with a history of urinary tract infection. Obstruction occurred in 23 infants (6.0/1000) and 16 required surgical correction. Vesicoureteric reflux was identified in 14 infants (3.6/1000) and resolved by age 2 years in 64%. Unilateral multicystic renal dysplasia occurred in 8 and posterior urethral valves occurred in 3 infants.

Conclusions: Antenatal ultrasonography after 28 weeks' gestation identified significant renal tract abnormalities with a frequency of 14.3 per 1000 births, permitting early treatment of the asymptomatic newborn and reducing later renal damage.