Objectives To determine the outcome of antenatally diagnosed hydronephrosis, including the analysis of the progression of the disease entity in utero, and ex- utero postnatal scans and surgical intervention.

Methods A retrospective audit of antenatal scans, which highlighted renal pelvic dilation (Antero-posterior diameter greater than 7 mm) at the second trimester scan and were referred for further assessment and follow up, during a period of one year (August 2011–July 2012), in a tertiary level university hospital.

Results 18 babies were identified with hydronephrosis from the second trimester scans. The AP diameter 7–10 mm was classed as moderate and >10mm was classed as severe. Of the 18 scans, 10 were severe and 7 were moderate and one had a renal abnormality. Third trimester scans revealed 10 severe, 5 moderate and 1 mild and two normal in severity. One patient was lost to follow up. Of the remaining 17, 78% had abnormal scans and 17% had normal postnatal scans.

Postnatal diagnoses included Multicystic dysplastic kidney (6), Posterior Urethral valves (1), Pelviureteric junction obstruction (2), Duplex kidney (1), Vesico-urethral reflux (3), Cross fused renal ectopia (1) Resolved cyst (1) Normal kidneys (2). 4 of the 17 required surgical intervention.

Conclusion Renal pelvic dilation of greater than 7 mm at the second trimester scans revealed the necessity for subsequent postnatal scans and follow up, in view of the significant postnatal findings requiring surgical follow up which were identified.

The importance of postnatal scans for identifying important conditions was highlighted.