Foetal Hydronephrosis and Urinary Tract Anomalies:Third Trimester Versus 20-week Scan

Abstract

Background and Aims: Foetal hydronephrosis may be associated with urinary tract disease and therefore a 20-week anomaly scan is recommended during pregnancy. Some reports have shown that ultrasound scanning later in pregnancy may also detect foetal hydronephrosis. In this study, we compare the incidence of urinary tract anomalies diagnosed following foetal hydronephrosis detected incidentally in late pregnancy versus at the recommended 20-week ultrasound scan. Material and Methods: A routine 20-week anomaly scan was performed on 4992 pregnant women, and if foetal hydronephrosis was present, a scan was repeated at 28 weeks. Persistence of hydronephrosis at 28 weeks defined Group A. Group B consisted of hydronephrotic foetuses discovered on incidental third trimester scan. The incidence of urinary tract anomalies detected postnatally was compared. Results: The findings in group A (n=44 infants) included: vesico-ureteric reflux (VUR) (1), pelvi-ureteric junction obstruction (1). In group B (12 infants, of whom 8 had an earlier normal 20-week scan) the findings included: VUR (2), multicystic dysplastic kidney (1), posterior urethral valve (1). The relative risk for VUR was 16.16 times higher (95% CI 0.80- 953.9) with hydronephrosis diagnosed in the 3rd trimester. Conclusion: The rate of urinary tract anomalies diagnosed after hydronephrosis on third trimester ultrasound scan is therefore higher than the recommended 20-week anomaly scan which may be falsely reassuring.