Fetal pyelectasis as predictor of decreased differential renal function.

Purpose: A decreased percent of differential function is a common indication for infant pyeloplasty but there is no recognized fetal ultrasound parameter to predict this deficit. We determined whether there is a correlation between fetal pyelectasis and the newborn percent differential function that may enhance prenatal counseling and guide postnatal evaluation.
Materials and Methods: Our database was queried for fetal and newborn measures with fetal pyelectasis on ultrasound and the percent of differential function on renal scintigraphy. Fetal pyelectasis data were stratified by estimated gestational age and the percent of differential function. The affected cohort was defined as having 35% or less differential function and the unaffected cohort was defined as having greater than 35%. The Wilcoxon 2-sample test was used for statistical analysis with logistic regression to generate estimated probability models of a decreased percent of differential function vs mm fetal pyelectasis.
Results: A total of 831 cases had fetal and newborn ultrasound data available with a total of 229 renal scans identified. Of the 229 cases 36 (16%) had 35% or less differential function on scintigraphy. At estimated gestational age 33 weeks or less the affected cohort had 8 mm greater pyelectasis than the unaffected cohort (OR 1.2, p <0.0001). At estimated gestational age greater than 33 weeks the affected cohort had 4 mm greater pyelectasis than the unaffected cohort (OR 1.07, p <0.07). Subgroup analysis before 33 weeks of estimated gestational age showed similar significance (OR >1, p <or=0.001).
Conclusions: Approximately 16% of all fetuses with pyelectasis have 35% or less differential function as newborns, including 36% identified by pyelectasis greater than 10 mm at estimated gestational age 20 to 24 weeks. Fetal pyelectasis greater than 10 mm at estimated gestational age 20 to 24 weeks and greater than 16 mm at greater than 33 weeks is associated with 35% or less differential function in the newborn.