Resistance index in fetal interlobar renal artery with renal pelvic dilatation up to 10 mm.

Purpose: The purpose of this study was to compare the resistance indices (RIs) in the fetal interlobar renal arteries (IRAs) of third-trimester fetuses with or without pelvicaliceal dilatation of up to 10 mm and to compare them with those of the full-term healthy infants.

Methods: Women with uncomplicated, low-risk, singleton third-trimester pregnancies were examined sonographically. The RIs in the IRAs were measured in the fetuses, who were stratified into 3 groups according to the anteroposterior diameter of the renal pelvic dilatation: group I, no dilatation; group II, 1-5-mm dilatation, and group III, 6-10-mm dilatation.

Results: In total, 178 women were examined. We could study both kidneys in 139 of the fetuses; in the other 39, only 1 kidney could be imaged perfectly. This yielded a total of 317 kidneys. Group I fetuses included 172 (54%); group II, 98 (31%); and group III, 47 (15%) of the kidneys. The mean (+/- standard deviation) RIs in the IRAs were 0.81 +/- 0.09, 0.80 +/- 0.07, and 0.80 +/- 0.06 in the 3 groups, respectively, with no statistically significant difference between the groups (p = 0.72). There was also no statistically significant difference between the RIs recorded in the right and left kidneys. The mean RI in the IRAs of the 34 infants who were available for follow-up 6-12 weeks after delivery was 0.73 +/- 0.07, which was significantly less than that recorded in the third-trimester fetuses (p = 0.005).

Conclusions: The RI in the fetal IRA does not differ in fetuses with and without renal pelvic dilatation of up to 10 mm. Thus, an increase in the RI or an RI that significantly differs between the right and left kidneys should be investigated further for possible renal pathology.