Minimal hydronephrosis in the fetus: Clinical significance and implications for management

Purpose: We further define the natural history and management of minimal fetal hydronephrosis. Materials and Methods: Experience with minimal fetal hydronephrosis (renal pelvic diameter 4 to 10 mm. before 20 weeks of gestation and 5 to 10 mm. from 20 to 24 weeks) was reviewed for 18 months at New England Medical Center. Results: The incidence of minimal fetal hydronephrosis was 2.2% in the 5,900 fetuses screened by ultrasound. In 63% of cases prenatal ultrasound was done more than once, and revealed that dilatation of the urinary tract was stable during gestation in 31 (25%), and became normal in 35 (29%) and worse in 11 (9%). A total of 63 patients (103 renal units) followed for up to 1 year underwent postnatal sonography. Those with abnormalities were screened with a voiding cystourethrogram and renal scan, including 40 with normal postnatal ultrasound and no changes on subsequent evaluation. Of the 23 patients with abnormal findings 4 had functionally significant ureteropelvic junction obstruction and 1 had severe vesicoureteral reflux. A retrospective analysis of the sonograms of patients with minimal fetal hydronephrosis and persistence or progression of hydronephrosis revealed calicectasis, progression of minimal fetal hydronephrosis in utero and/or abnormal renal echogenicity in each fetus. Conclusions: Our study shows that in a small but significant number of fetuses minimal fetal hydronephrosis will progress, whereas in most it will resolve.