The accuracy of antenatal ultrasonography in identifying renal abnormalities.

OBJECTIVE: To determine the accuracy of measuring antenatal renal pelvic diameter for prediction of renal abnormalities.

RESEARCH DESIGN: Prospective evaluation of all pregnant women undergoing ultrasonography.

SETTING: A teaching hospital providing primary and referral maternity care.

PARTICIPANTS: Fifty-six pregnant women with suspected fetal hydronephrosis or cystic lesions identified from 7500 ultrasonograms over 3 years.

METHODS: Antenatal renal pelvic diameter was measured in the anteroposterior dimension. Neonates underwent postnatal ultrasonography after day 3 of life; if the results were abnormal, a cystogram and renal diuretic scan were obtained.

RESULTS: None of 50 kidneys 15 mm or smaller in anteroposterior pelvic diameter had obstruction; 11 (79%) of 14 kidneys larger than 15 mm were obstructed or demonstrated vesicoureteral reflux. Of 12 kidneys believed to be multicystic before birth, five (42%) proved to have hydronephrosis.

CONCLUSIONS: Since the majority of fetuses with suspected hydronephrosis proved to be normal, parents should not be unduly alarmed by the physician. Renal pelvic diameter of more than 15 mm is strongly predictive of hydronephrosis. Since severe hydronephrosis is treatable and can be mistaken for a multicystic kidney antenatally, full radiologic evaluation is needed soon after birth.