Fetal pyelectasis: is it always "physiologic"?

Our purpose was to determine the degree of fetal pyelectasis predictive of neonatal renal pathologic processes.

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.

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.

Fetuses with an anteroposterior diameter of the renal pelvis > or = 8 mm after 28 weeks' gestation require appropriate urologic evaluation after birth.