The type and frequency of fetal renal disorders and management of renal pelvis dilatation.

Objective: This study describes the frequency of sonographically detected fetal renal disorders, the correlation of fetal renal pelvis dilatation (RPD) with the need for postnatal surgery, and proposed management of RPD.
Methods: The study population consisted of 342 fetuses with prospectively identified isolated renal abnormalities and known follow-up. Fetuses with RPD were considered separately with respect to underlying renal disease, postnatal testing, and the need for surgical correction. Obstructive RPD was defined as the need for surgical treatment. Nonobstructive RPD included those cases that required no therapy. The correlation between prenatal RPD and the need for postnatal evaluation was examined.
Results: Renal pelvis dilatation was the primary postnatal sonographic finding in 66.4% of cases. The remainder were distributed between multicystic dysplastic kidney, duplication malformations, and reflux, with a smaller number of other diagnoses. Renal pelvis dilatation in the obstructive group was significantly greater than in the nonobstructive group. However, 10% of fetuses with maximum RPD of 10 mm or less had an obstructive process, whereas 58% of fetuses with RPD of greater than 10 mm did not have obstruction. There were no cases in which preterm delivery was necessitated by RPD.
Conclusions: Renal pelvis dilatation is the most common fetal renal abnormality. The greater the RPD, the more likely it is due to obstruction. However, the overlap between obstruction and no obstruction dictates postnatal evaluation. In that RPD, regardless of degree, did not change the timing of delivery, a single follow-up sonographic examination either late in pregnancy or after delivery is considered adequate for follow-up of RPD detected earlier in pregnancy.