Objective Fetal hydronephrosis is the most common fetal abnormality detected on antenatal ultrasound scans. We looked at the pattern and prevalence of RPD on antenatal screening, and the postnatal outcome in our local catchment area.

Methods This was a retrospective study covering all cases of antenatally detected RPD (defined as over 4 mm) between January 2003 and December 2004. Information was obtained from identified mothers’ and babies’ notes, and from the postnatal ultrasound scan reports.

Results Out of 7041 live births in the two year period, 108 cases had antenatally detected RPD. 78% of these cases were bilateral and the vast majority were between 5 and 15 mm. Over half of them had reverted to normal on follow-up antenatal scans. The male to female ratio was 1.8:1. 42% had normal first postnatal scan (<9 mm). Babies with RPD ⩾9 mm showed significant abnormalities like pelvi-ureteric obstruction obstruction, vesico-ureteric reflux, duplex kidney, baggy pelvis with no obstruction and congenital hydronephrosis (total 11 cases).

Conclusion There is a prevalence of antenatal RPD of about 1.5% in our population. Those who reverted to normal on follow up antenatal and postnatal scans had RPD <9 mm. Also, babies diagnosed with idiopathic RPD had no episode of UTI and subsequently reverted to normal by 2 years of age which is in line with findings of other studies. There is a concern about the relationship between antenatally detected renal pelvis dilatation and vesico-ureteric reflux, but this has not been illustrated in our study.