Fetal hydronephrosis as a predictor of neonatal urologic outcomes

The ability to predict surgically relevant fetal renal hydronephrosis is limited. We sought to determine the most efficacious second- and third-trimester fetal renal pelvis anteroposterior diameter cutoffs to predict the need for postnatal surgery.

We retrospectively reviewed the medical records of mothers and neonates who had a prenatal sonographic examination in our Perinatal-Pediatric Urology Clinic and received follow-up care. Hydronephrosis was defined as a renal pelvis anteroposterior diameter of 5 mm or greater in the second trimester and 7 mm or greater in the third trimester. Hydronephrosis was subdivided into mild, moderate, and severe.

Of 8453 fetuses, 96 met the criteria and were referred to our clinic. Isolated hydronephrosis was diagnosed in 74 fetuses, of which 53 received postnatal follow-up evaluations. The areas under the receiver operating characteristic curves for predicting postnatal surgery in the second and third trimesters were 0.770 and 0.899, respectively. The second-trimester renal anteroposterior diameter threshold that best predicted post-natal surgery was 9.5 mm (sensitivity, 71.4%; specificity, 81.1%). The third-trimester threshold that best predicted postnatal surgery was 15.0 mm (sensitivity, 85.7%; specificity, 94.6%).

The fetal renal anteroposterior diameter on second- and third-trimester sonography is predictive of an increased risk for neonatal urologic surgery. Surgical risk is best predicted by a third-trimester renal anteroposterior diameter threshold of 15 mm.