Management of Newborn with Right-Sided Hydronephrosis and Single Umbilical Artery

Initial Assessment and Management

The American College of Radiology recommends performing a postnatal renal and bladder ultrasound at 48-72 hours of life to confirm the hydronephrosis and assess severity, followed by a third-trimester growth ultrasound and consideration of weekly antenatal surveillance beginning at 36 weeks gestation for the single umbilical artery finding 1, 2
Delay initial imaging until 48-72 hours after birth unless there are concerning features, and perform a complete renal and bladder ultrasound with the infant well-hydrated and bladder distended 3
Classify severity using Society for Fetal Urology (SFU) grading or anteroposterior renal pelvis diameter (APRPD), with grade 3-4 or APRPD >15 mm indicating severe hydronephrosis 4

For mild hydronephrosis (SFU Grade 1-2 or APRPD <10 mm), follow-up ultrasound at 1-6 months to reassess, with no immediate intervention required unless clinical deterioration occurs 1, 5, 6, 7
For moderate to severe hydronephrosis (SFU Grade 3-4 or APRPD >15 mm), voiding cystourethrography (VCUG) at approximately 1 month of age to evaluate for vesicoureteral reflux (VUR) and exclude posterior urethral valves if male, and consider prophylactic antibiotics 1, 6, 5, 4
MAG3 renal scan at 2+ months of age to assess split renal function and drainage, particularly if obstruction is suspected 6, 4
Diuretic renography helps differentiate true obstruction from non-obstructive dilation, with T1/2 >20 minutes indicating true obstruction 7, 4

No additional aneuploidy evaluation is needed for isolated single umbilical artery, regardless of prior screening, and the presence of single umbilical artery does not change the hydronephrosis workup algorithm 2
Third-trimester ultrasound to evaluate fetal growth, and consider weekly antenatal fetal surveillance beginning at 36 0/7 weeks gestation to monitor for intrauterine growth restriction 2

Repeat ultrasound at 1-6 months after initial postnatal scan, and for persistent hydronephrosis, ultrasound monitoring at least once every 2 years to assess for progression 1, 6, 5, 4
Serial MAG3 scans if obstruction is confirmed, watching for >5% decrease in differential renal function as indicator for surgical intervention 7, 4

Surgery is indicated when there is evidence of T1/2 of time activity curve >20 minutes on diuretic renography, decreased renal function (<40% differential function), deteriorating function (>5% change on consecutive renal scans), or worsening drainage on serial imaging 7, 4