Antenatally detected urinary tract abnormalities: changing incidence and management

To define the incidence of urinary tract abnormalities detected by antenatal ultrasound and assess changes in postnatal management we conducted a retrospective survey using data bases of the nephro-urology unit, obstetric ultrasound and perinatal pathology departments. The birth population (105,542) of the two Nottingham teaching hospitals between January 1984 and December 1993 was divided into two 5-year cohorts, 1984-1988 and 1989-1993. Detailed fetal scanning at 18-20 weeks gestation was introduced in 1989. During this 10-year period, 201 abnormalities of the urinary tract were noted with a 2:1 male to female ratio. The incidence of abnormalities in the first 5 years was 1 in 964 compared to 1 in 364 in the last 5 years. There was a significant increase in the number detected before 20 weeks gestation (12% in 1984-1988 compared to 62% in 1989-1993). Despite the increased incidence of abnormalities detected, the termination rate remained static between the two 5-year cohorts. Only 3 fetuses had intra-uterine intervention and 173 were live-born. Eight infants subsequently died in association with other major congenital abnormalities. The incidence of transient abnormalities (antenatal dilatation with no abnormality noted on postnatal ultrasound) increased from 6% in 1984-1988 to 18% in the 1989-1993 cohort. A more conservative approach to postnatal management is reflected by 71% of infants having operations between 1984 and 1988 compared to 35% in 1989-1993.

The advent of detailed fetal scanning at 18-20 weeks gestation has significantly increased the detection rate of urinary tract abnormalities with no significant increase in pregnancy termination rates. The need for antenatal intervention is a rare event and most problems can be managed conservatively both pre- and postnatally.