Outcome of isolated fetal renal pyelectasis diagnosed during midtrimester screening ultrasound and cut-off value to predict a persistent or progressive pyelectasis in utero

Aim: To define a better cut-off value of the renal pelvis anteroposterior diameter (RPAPD) to predict persistent or progressive pyelectasis during pregnancy. Methods: We retrospectively reviewed 8873 women whose fetal RPAPD was measured. Midtrimester pyelectasis was defined as a RPAPD of ≥4 mm. Persistent/progressive pyelectasis was defined as a RPAPD of ≥10 mm before delivery. A RPAPD cut-off value to predict a persistent/progressive pyelectasis was determined by receiver operating characteristic curve analysis. Results: Among 249 isolated cases of pyelectasis, persistent/ progressive pyelectasis was found in 6.9 % before delivery. The midtrimester RPAPD cut-off value that best predicted persistent/progressive pyelectasis before delivery was ≥6 mm with sensitivity, specificity, positive and negative predictive values of 64.3 % , 88.7 % , 30.0 % , and 97.1 % , respectively. Conclusions: Although most cases of midtrimester fetal pyelectasis regress to normal during pregnancy, those with a RPAPD of ≥6 mm in the midtrimester are at higher risk for persistent or progressive pyelectasis.