What is the recommended follow‑up and management for a fetus diagnosed with a single umbilical artery (SUA)?

Management of Single Umbilical Artery

For isolated single umbilical artery (SUA), perform a comprehensive cardiac anatomy assessment at the time of diagnosis, obtain a third-trimester ultrasound to evaluate fetal growth, and consider weekly antenatal fetal surveillance beginning at 36 0/7 weeks of gestation. 1

Initial Evaluation and Risk Stratification

When SUA is detected on second-trimester ultrasound, the critical first step is distinguishing isolated SUA from SUA with associated abnormalities, as this fundamentally changes management and prognosis. 1

Structural Anomaly Assessment

• Perform a comprehensive assessment of cardiac anatomy using a standard 76811 ultrasound examination at the time of SUA diagnosis 1
• If required cardiac views are adequately visualized and normal, fetal echocardiography is not routinely warranted 1
• However, if additional risk factors for congenital heart disease are present beyond the SUA, referral for fetal echocardiography is indicated 2
• Co-occurring structural abnormalities most commonly involve the cardiovascular and renal systems 1, 3, 4

Important caveat: When SUA occurs with one or multiple structural abnormalities, the frequency of associated aneuploidy ranges from 4% to 50%, making genetic evaluation essential in non-isolated cases. 1

Aneuploidy Risk Assessment

For fetuses with isolated SUA, no additional evaluation for aneuploidy is recommended, regardless of whether previous aneuploidy screening results were low risk or screening was declined. 1

This recommendation is based on evidence showing that isolated SUA does not confer increased risk of aneuploidy. 1 This contrasts sharply with non-isolated SUA, where aneuploidy risk is substantially elevated. 1

Third-Trimester Surveillance

The evidence regarding fetal growth restriction (FGR) in isolated SUA is conflicting—some studies show increased risk while others do not. 1 However, given the demonstrated association with stillbirth (OR 4.80; 95% CI 2.67-8.62) and potential risks of FGR, polyhydramnios, oligohydramnios, placental abruption, and cord prolapse, the Society for Maternal-Fetal Medicine recommends a cautious approach. 1

Growth Monitoring

• Obtain a third-trimester ultrasound examination to evaluate fetal growth 1
• This recommendation stands despite some studies showing no increased incidence of FGR in isolated SUA cohorts 1, 5
• Research shows that when FGR does occur with isolated SUA, it is associated with lower birth weight (approximately 150-400g less than controls) 3, 4

Antenatal Fetal Surveillance

• Consider weekly antenatal fetal surveillance beginning at 36 0/7 weeks of gestation for fetuses with isolated SUA 1
• This recommendation is driven by the nearly 5-fold increased odds of stillbirth compared to pregnancies with a three-vessel cord 1

Delivery and Postnatal Management

Communication with Pediatric Team

• At the time of delivery, notify the pediatric provider of the prenatal SUA findings 1
• This notification is important because postnatal examination reveals structural anomalies in up to 7% of infants with prenatal diagnosis of isolated SUA 1, 4
• These anomalies may not have been detected on prenatal imaging 1

Systems to Evaluate Postnatally

When structural anomalies are discovered postnatally in cases of prenatally diagnosed isolated SUA, they most commonly involve:

• Urinary system (highest incidence) 3, 6
• Cardiovascular system 3, 4, 6
• Digestive/gastrointestinal system 3, 4, 6
• Musculoskeletal system 4, 6

Key Clinical Pearls

Common pitfall: Assuming all SUA cases require fetal echocardiography. The evidence shows that in low-risk fetuses with isolated SUA and adequate visualization of cardiac anatomy on standard obstetric ultrasound, echocardiography may not provide additional benefit. 1, 2

Reassuring finding: Recent large population-based studies show weak or no associations between isolated SUA and most neurodevelopmental disorders, with the exception of modest associations with intellectual disability and ADHD that appear sex-dependent and are not mediated significantly by preterm birth or small-for-gestational-age status. 7

Laterality note: Right-sided SUA is more common than left-sided (approximately 60-64% vs 36-40%), though this does not appear to impact clinical management. 3, 4