Fetal pyelectasis: is it always "physiologic"?

Objective: Our purpose was to determine the degree of fetal pyelectasis predictive of neonatal renal pathologic processes.
Study Design: Eighty-four cases of pyelectasis were identified during the study period (1989 through 1993). Fetuses with anteroposterior diameter of the renal pelvis > or = 4 mm before 33 weeks or > or = 7 mm after 33 weeks without caliectasis were included. Fetuses with an anteroposterior diameter of > 10 mm were excluded. Postnatal evaluation included renal sonogram, voiding cystourethrogram, and renal flow and function studies.
Results: Sixteen cases were excluded because of incomplete postnatal workup. Renal pathologic processes were found in 30 of 68 (44%) at birth; the most common were ureteropelvic junction obstruction (37%) and vesicoureteral reflux (33%). Only four cases required surgical intervention (13%), and the remaining 87% were managed conservatively. A normal urinary tract was found in 25% of the infants and the remaining 21 of 68 (31%) had regression of pyelectasis before birth. Fetuses with a dilated anteroposterior diameter > or = 8 mm after 28 weeks' gestation were found to have renal pathologic features in two of three of the cases, with sensitivity, specificity, and positive and negative predictive values of 87%, 41%, 66.7% and 70%, respectively.
Conclusion: Fetuses with an anteroposterior diameter of the renal pelvis > or = 8 mm after 28 weeks' gestation require appropriate urologic evaluation after birth.