Follow-Up Timing for Isolated Single Umbilical Artery
For isolated single umbilical artery (SUA), perform a third-trimester ultrasound to evaluate fetal growth, and consider initiating weekly antenatal fetal surveillance beginning at 36 0/7 weeks of gestation. 1, 2
Initial Assessment Requirements
When SUA is first identified on second-trimester ultrasound, immediate evaluation is necessary:
- Perform a comprehensive assessment of cardiac anatomy using the standard anatomy scan (CPT 76811), as cardiovascular and renal systems are most commonly affected when SUA occurs with structural abnormalities 1, 2
- Fetal echocardiography is NOT routinely warranted if the cardiac views on the anatomy scan are adequately visualized and normal 1, 2
- No additional aneuploidy evaluation is needed for isolated SUA, regardless of whether previous aneuploidy screening was negative, low-risk, or declined, as isolated SUA shows no increased risk of aneuploidy 1, 2
Third-Trimester Surveillance Protocol
The Society for Maternal-Fetal Medicine provides clear guidance on timing:
- Schedule a third-trimester ultrasound examination specifically to evaluate fetal growth, as this is when growth restriction becomes clinically significant 1, 2
- Begin weekly antenatal fetal surveillance at 36 0/7 weeks of gestation due to increased risks of stillbirth (OR 4.80), polyhydramnios, oligohydramnios, placental abruption, cord prolapse, and perinatal mortality 1, 2
Rationale for Enhanced Surveillance
The evidence supporting this approach is based on conflicting but concerning data:
- Research demonstrates that isolated SUA is independently associated with intrauterine growth restriction (IUGR) in 15.4% of cases (adjusted OR 11.3) and very preterm delivery in 6.6% of cases (adjusted OR 5.0) 3
- Population-based studies show a significantly increased odds ratio for stillbirth compared to live birth (OR 4.80,95% CI 2.67-8.62) 1
- While some studies suggest no increased risk of growth restriction, the preponderance of evidence and potential for adverse outcomes justifies enhanced surveillance 1
Postnatal Considerations
- Notify the pediatric provider at delivery of the prenatal SUA finding, as postnatal examination reveals structural anomalies in up to 7% of infants despite prenatal diagnosis of "isolated" SUA 1, 2
Common Pitfalls to Avoid
- Do not perform fetal echocardiography routinely if the anatomy scan cardiac views are adequate and normal—this represents unnecessary testing 1, 2
- Do not pursue additional aneuploidy testing (amniocentesis or cell-free DNA) for isolated SUA, as this finding alone does not increase aneuploidy risk 1, 2
- Do not delay third-trimester growth assessment—the timing is critical for detecting growth restriction that may develop later in pregnancy 2, 3
- Be vigilant if follow-up ultrasound shows apparent conversion from two arteries to one artery, as this may represent umbilical artery thrombosis requiring immediate intervention 4