Fetal hydronephrosis: optimal renal pelvic measurement to increase detection rate for renal pathology.

We reviewed the outcome of fetal hydronephrosis with a renal pelvic dilatation (RPD) of 4-7 mm to assess whether a RPD > 7 mm had a higher predictive value for renal pathology. 373 fetuses were diagnosed with hydronephrosis giving an incidence of 2.2%. The male: female ratio was 1.8:1. 5(1.34%) fetuses with antenatal hydronephrosis were diagnosed with Down Syndrome. 299 (91.7% fetuses with an RPD of 4-7 mm had resolved by 34 weeks gestation with 10 (3.1%) having moderate to severe hydronephrosis. The resolution rate for RPD > 7 mm was 60.7% (17) with 11 fetuses (39.3%) requiring long term follow up.