Clinical relevance and implications of antenatal hydronephrosis.

Detailed antenatal sonography was performed on 18766 pregnant women between 1990 and 1994. Antenatal hydronephrosis, defined as an antero-posterior diameter of the renal pelvis (APPD) greater than 5 mm, was detected in 100 cases (0.59%). Sixty four infants had postnatal hydronephrosis at one and/or six weeks after delivery; 21 of these had urological anomalies. Twelve infants had vesico-ureteric reflux. In all refluxing units the APPD of the renal pelvis was less than 10 mm. Three patients had obstruction at the pelviureteric junction (PUJ); all required surgery. Vesico-ureteric reflux is emerging as the most common urological finding in infants with antenatal hydronephrosis and is likely to be missed if kidneys with APPD of less than 10 mm are not further investigated. In contrast, pelvi-ureteric junction obstruction may be overdiagnosed, based only on drainage patterns of dynamic renogram studies.