Antenatal hydronephrosis: thresholds of renal pelvic diameter to predict insignificant postnatal pelviectasis.

We tested the parameters of gestational age and renal pelvic anteroposterior (AP) diameter of antenatally detected pelvicaliectasis for their ability to determine insignificant postnatal renal pelvic dilatation. A retrospective analysis of 10,365 antenatal sonograms revealed 121 kidneys with pelvicaliectasis, from which 99 sonograms with sufficient postnatal follow-up were reviewed. Gestational ages were classified as <20, 20-30, or >30 weeks. Thresholds of renal pelvic AP diameter in each gestational period that were predictive of postnatal insignificance were determined to be <6, <8, and <10 mm, respectively. Insignificance postnatally was defined as no or minimal renal pelvic splitting (Society for Fetal Urology grade <II/IV). By categorizing the antenatal sonograms into gestational periods and varying the threshold of AP diameter in each period, the overall sensitivity, specificity, positive predictive value, and negative predictive value of these parameters were 89%, 96%, 95%, and 91%, respectively. We conclude that applying these parameters to antenatal pelvicaliectasis could ultimately provide a clinical management strategy that would aid in the prediction of an insignificant postnatal outcome and obviate unnecessary investigations, anxiety, and cost.