Diagnostic accuracy of fetal renal pelvis anteroposterior diameter as a predictor of significant postnatal nephrouropathy: second versus third trimester of pregnancy.

Objective: The objective of the study was to determine the most effective fetal renal pelvis anteroposterior diameter thresholds and the best gestational age in predicting significant neonatal nephrouropathy and neonatal nephrouropathy requiring surgery.

Study Design: Eighty-three newborns with prenatal ultrasound evidence of unilateral or bilateral fetal renal pelvis dilatation (anteroposterior diameter 4 mm or more) before the 26th week of gestation were systematically and prospectively investigated prenatally and postnatally.

Results: Receiver operating characteristic curve analysis showed that third-trimester anteroposterior diameter cut-offs were more reliable than second-trimester cut-offs in predicting significant neonatal nephrouropathy, the best threshold being 8 mm. No significant differences were found between the 2 trimesters in the screening of fetuses at risk of neonatal nephrouropathy requiring surgery.

Conclusion: Significant neonatal nephrouropathy is better predicted at the third trimester, the best threshold being 8 mm, but the screening of patients at greater risk of surgery is also possible during the second trimester. An anteroposterior diameter of 11 mm or more, with an odds ratio of 128.33 (95% confidence interval 11.68 to 1408.98), is a very effective cut-off and a reliable prognostic indicator of neonatal nephrouropathy requiring surgery, even before the 26th week.