Prenatal Mild Pyelectasis: Evaluating the Thresholds of Renal Pelvic Diameter Associated with Normal Postnatal Renal Function

Objective. To determine the threshold of the renal pelvic anteroposterior (AP) diameter that predicts normal postnatal renal outcome in the follow-up of cases with mild pyelectasis. Methods. A retrospective review of our sonography database was conducted over a 3-year period for cases of mild pyelectasis diagnosed between 18 and 30 weeks. Cases were evaluated for the association between different thresholds of renal pelvic anteroposterior diameter and normal postnatal function after 32 weeks' gestation and also for the initial renal pelvic anteroposterior diameter at 18 to 30 weeks. Results. In the 3-year period, 7416 women were evaluated, and 150 cases with a diagnosis of pyelectasis (2%) were identified. Among the 115 women meeting our inclusion criteria, complete outcomes were available for 66. Persistent postnatal renal anomalies were seen in 20 cases (30%). On the basis of receiver operating characteristic curves, the renal threshold that best predicted normal postnatal outcome was an anteroposterior diameter of less than 7.0 mm after 32 weeks, yielding sensitivity and specificity of 87% and 85%, respectively (odds ratio, 0.31; 95% confidence interval, 0.11-0.86; P < .02). Conclusions. In the follow-up of fetuses with a diagnosis of mild pyelectasis between 18 and 30 weeks, a renal pelvic anteroposterior diameter of less than 7.0 mm after 32 weeks is highly predictive of normal postnatal renal function. Therefore, only those with an anteroposterior diameter of greater than 6 mm after 32 weeks deserve follow-up.