Renal ultrasonography in newborns with prenatally detected hydronephrosis: Why wait?

Purpose: Published reports suggest the need to delay renal ultrasound for at least 1 week after birth to avoid a false-negative study due to oliguria. This recommendation has become standard. Considering the recent shift toward expectant management of prenatal hydronephrosis, there may be no advantage to the increased sensitivity of a delayed study. Materials and Methods: Radiology records were reviewed for a 5-year period to identify renal ultrasound studies performed within 48 hours of birth. Results: Of 101 neonates known to have hydronephrosis on prenatal ultrasound who underwent sonography within 48 hours of birth 33 had a normal study (including mild hydronephrosis) and documented followup studies. None of these patients had a significant obstructive renal lesion within the first year of life. One child had an obstructive pattern on diuretic renography at age 18 months after previous studies were unremarkable. Cystography in 26 patients demonstrated vesicoureteral reflux in 4 (14.3%). Conclusions: These data suggest that 1) there is no contraindication to early neonatal renal ultrasonography and 2) voiding cystourethrography is indicated for all infants with a history of prenatal hydronephrosis.