What is the treatment plan for a newborn with right-sided hydronephrosis and a single umbilical artery (SUA) diagnosed on antenatal scan?

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

Perform 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

Immediate Postnatal Assessment

Initial Ultrasound Timing and Evaluation

• Delay initial imaging until 48-72 hours after birth unless there are concerning features such as severe bilateral hydronephrosis, bladder abnormalities, or oligohydramnios history, which would require immediate evaluation 2
• The delay accounts for relatively low urine production in the immediate postnatal period that can underestimate the severity of hydronephrosis 2
• Perform a complete renal and bladder ultrasound (not just limited renal imaging) with the infant well-hydrated and bladder distended 2
• Classify severity using Society for Fetal Urology (SFU) grading (grade 3-4 is severe) or anteroposterior renal pelvis diameter (APRPD >15 mm indicates severe hydronephrosis) 3

Physical Examination Priorities

• Assess for respiratory distress or abdominal mass effect from severe hydronephrosis 4
• Examine for other congenital anomalies, as single umbilical artery can be associated with additional abnormalities 5
• Monitor voiding patterns and urine output in the first 24-48 hours 4
• Check serum creatinine levels and monitor decay curve corresponding to gestational age to evaluate renal function 4

Management Based on Severity

Mild Hydronephrosis (SFU Grade 1-2 or APRPD <10 mm)

• Follow-up ultrasound at 1-6 months to reassess 1
• No immediate intervention required unless clinical deterioration occurs 1
• Consider prophylactic antibiotics, though benefit remains unclear 1

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 1
• VUR accounts for 30% of urinary tract abnormalities in infants with antenatal hydronephrosis 1
• Consider prophylactic antibiotics while awaiting VCUG, as there is higher risk for urinary tract infection 1, 3
• MAG3 renal scan at 2+ months of age (preferred over DTPA) to assess split renal function and drainage, particularly if obstruction is suspected 1, 3
• Diuretic renography helps differentiate true obstruction (T1/2 >20 minutes) from non-obstructive dilation 1, 3

Urgent Indications Requiring Immediate Intervention

• Bladder catheterization immediately at birth if there is high suspicion for posterior urethral valves (bladder wall thickening, dilated posterior urethra on ultrasound) 1, 2
• Mass effect causing respiratory compromise or circulatory instability 4
• Rising serum creatinine indicating renal dysfunction 4
• Signs of urinary tract infection or sepsis 3, 4
• Immediate urology referral if posterior urethral valves are confirmed 1

Single Umbilical Artery Specific Management

Postnatal Evaluation

• No additional aneuploidy evaluation is needed for isolated single umbilical artery, regardless of prior screening 1
• The presence of single umbilical artery does not change the hydronephrosis workup algorithm 1
• While some older studies suggested screening all infants with isolated single umbilical artery for renal anomalies, more recent evidence shows this is not necessary when physical examination is normal 6
• However, given the antenatal detection of hydronephrosis in this case, full evaluation of the hydronephrosis is warranted regardless of the single umbilical artery 5, 7

Growth Monitoring

• Third-trimester ultrasound to evaluate fetal growth 1
• Consider weekly antenatal fetal surveillance beginning at 36 0/7 weeks gestation 1
• Monitor for intrauterine growth restriction 1

Follow-Up Protocol

Serial Imaging Schedule

• Repeat ultrasound at 1-6 months after initial postnatal scan 1
• For persistent hydronephrosis, ultrasound monitoring at least once every 2 years to assess for progression 3
• Serial MAG3 scans if obstruction is confirmed, watching for >5% decrease in differential renal function as indicator for surgical intervention 1, 3

Surgical Intervention Criteria

Surgery is indicated when there is evidence of:

• T1/2 of time activity curve >20 minutes on diuretic renography 1, 3
• Decreased renal function (<40% differential function) 1, 3
• Deteriorating function (>5% change on consecutive renal scans) 1, 3
• Worsening drainage on serial imaging 1, 3

Common Pitfalls to Avoid

• Do not perform ultrasound in the first 24-48 hours unless urgent indications exist, as this can underestimate severity due to low neonatal urine production 2
• Do not assume normal postnatal ultrasound excludes urinary tract abnormality - 45% of infants with normal first ultrasound were later diagnosed with urinary tract abnormalities 7
• Do not delay VCUG in male infants with moderate-severe hydronephrosis, as posterior urethral valves require immediate intervention 1, 2
• Do not rely on single umbilical artery alone to determine need for renal imaging - the antenatal hydronephrosis is the primary indication for full workup 1, 6
• Do not use DTPA renal scan when MAG3 is available, especially with suspected obstruction or impaired function 1, 3