Fetal hydronephrosis: does adding an extra parameter improve detection of neonatal uropathies?

OBJECTIVE: The aim of this study is to assess the correlation of the average antero-posterior, transverse and longitudinal diameters of the fetal renal pelvis to neonatal outcome. METHODS: This retrospective study evaluates the neonatal outcome of all fetuses with suspected pyelectasis on ultrasonographic examination between May 1997 and March 2006. During this time, 764 fetuses with pyelectasis and 1285 renal units were scanned. We defined fetal pyelectasis as mild if the ARP was ≥ 5-<10 mm, moderate if ARP ≥ 10-<15 mm and severe if ARP ≥ 15 mm. A total of 612 fetuses met the inclusion criteria. The Corteville criteria in the third trimester (antero-posterior diameter ≥ 7 mm) and an antero-posterior diameter (AP) of ≥ 10 mm were compared with the ARP and likelihood ratio's calculated. Ultrasonographic evaluation took place in the third trimester if fetal pyelectasis was diagnosed as an isolated finding in the second trimester. This last ultrasonographic examination was used for final analysis and as a guideline for postnatal follow-up. Neonatal outcome was assessed by reviewing medical records, ultrasonographic, renographic and voiding cysto-urethrographic results. RESULTS: Of all the fetuses diagnosed with renal pelvis dilatation in the third trimester of pregnancy, 73 (11.9%) infants needed postnatal surgery. The majority of the postnatal surgery was performed in the group of fetuses with severe hydronephrosis (8.2%). This resulted in a LR of 5.81 and a post-test probability of 61.3%. In total, 78.8% of the fetuses with hydronephrosis had spontaneous resolution across all grades of severity on the first postnatal ultrasonogaphic investigation or during their follow-up. In 9.3% of the cases, uropathies were diagnosed, but no surgical intervention had taken place during the follow-up period. Using the Corteville criteria as gold standard for the third trimester (AP ≥ 7 mm), 11 (1.8%) patients would not have been diagnosed with uropathies. And in the case of AP ≥ 10 mm, 5.1% of the cases would have been missed. CONCLUSION: An ARP of ≥ 5 mm in the second and/or third trimester of pregnancy enables a better detection of patients with uropathies and indication for surgery as compared with AP ≥ 10 mm, but renders almost similar results compared with the Cortville criteria (AP ≥ 7 mm) in the third trimester.