[Post-natal diagnostic strategy of urinary tract malformations detected by prenatal screening]

The increasing experience with prenatal ultrasonographic diagnosis allows detection of more and more mild urinary tract anomalies. Thus, the clinical significance of many pyelectasis detected before birth is not known.

From a retrospective study of 78 patients, we determined the positive predictive value (PPV) of prenatal ultrasound findings for urinary tract malformations.

This PPV was 27.3% when the prenatal pelvic dilatation was isolated, but grew up to 100% if a caliceal dilatation was associated. Renal pelvic diameter in the third trimester of pregnancy could predict the degree of post-natal renal impairment, as pelvic size was 6.7 +/- 2.15 mm for the post-natal pyelectasis group, significatively smaller than 13.4 +/- 3 mm in the ureteropelvic junction obstruction group (grade 1) and than 17 +/- 9 mm in other pathological renal units. On the other hand, antenatal ultrasound had a bad sensibility for vesico-ureteral reflux detection, four primary reflux among 14 being detected without homolateral antenatal ultrasound anomaly.

According these results, we propose a post-natal diagnostic strategy. Urological explorations are performed when the prenatal renal pelvic diameter is larger than 10 mm. If the postnatal ultrasound shows an isolated pyelectasis below this level, a clinical follow-up is advised, the parents being informed of the possibility of vesico-ureteral reflux and of the necessity to perform a cytobacteriological exam of urines in case of unexplained fever.