Natural history of bilateral mild isolated antenatal hydronephrosis conservatively managed

The purpose of this study was to assess the prevalence and outcome of newborns with bilateral mild isolated antenatal hydronephrosis managed with neither antibiotic prophylaxis nor voiding cystourethrography (VCUG). Inclusion criteria were ultrasonographic evidence of an anterior-posterior pelvic diameter (APPD) of 5-15 mm at the third trimester of gestation and on the first postnatal ultrasound sonogram. Exclusion criteria were an APPD > 15 mm, calyectasis, hydroureteronephrosis, or renal or bladder abnormalities. Ultrasound follow-up was performed. Parents were familiarized with the signs of urinary tract infection (UTI). If UTI was confirmed, VCUG was performed. The outcome was assessed as intrauterine resolution of hydronephrosis, total or partial resolution, stability, or progression. Hydronephrosis was bilateral in 98 of the 236 newborns (196 hydronephrotic kidneys) with mild isolated antenatal hydronephrosis enrolled in this study. Nine patients had UTI, and none showed reflux. After a mean follow-up of 15 months, 74 kidneys showed intrauterine resolution (38%), 82 (42%) showed total resolution, 13 showed partial resolution, 24 were stable, and 3 showed progression. Bilateral cases represented 42% of mild isolated antenatal hydronephrosis. During the first year of life, 80% of the kidneys showed total hydronephrosis resolution, 9% of patients had UTI, and none of the patients showed reflux. Antibiotic prophylaxis and VCUG are not mandatory in newborns with bilateral mild isolated antenatal hydronephrosis, but clinical and ultrasound follow-up are recommended during the first year of life.