What is the recommended management for a fetus with a single umbilical artery detected on prenatal ultrasound?

Management of Single Umbilical Artery

For a fetus with isolated single umbilical artery (SUA) detected on prenatal ultrasound, perform a comprehensive cardiac and renal anatomic assessment immediately, then schedule third-trimester growth ultrasound and weekly antenatal surveillance starting at 36 weeks—no additional aneuploidy testing is needed regardless of prior screening status. 1, 2

Initial Diagnostic Workup

Comprehensive Anatomic Survey

• Perform detailed cardiac assessment on the anatomy scan focusing on cardiovascular structures, as cardiac anomalies are the most common associated finding with odds ratios ranging from 5.9 to 20.3 for various cardiac defects 3, 4
• Evaluate renal anatomy thoroughly, as renal anomalies show a 3-fold increased risk with approximately 16% of isolated SUA cases having some form of renal abnormality 3
• If required cardiac views are adequately visualized and normal on the anatomy scan, fetal echocardiography is not routinely warranted 1, 2

Distinguish Isolated vs. Non-Isolated SUA

• Isolated SUA = no other structural or chromosomal abnormalities present 1
• Non-isolated SUA = SUA with one or multiple structural abnormalities, which carries aneuploidy risk of 4-50% 1, 3

Aneuploidy Risk Assessment

For isolated SUA, no additional evaluation for aneuploidy is recommended, regardless of whether previous aneuploidy screening results were low risk or screening was declined. 1, 2 This is a firm recommendation because:

• Isolated SUA shows no increased risk of aneuploidy 1, 3
• Diagnostic testing solely for isolated SUA wastes resources and causes unnecessary anxiety 2
• However, if SUA occurs with other structural abnormalities, the aneuploidy frequency ranges from 4-50%, warranting genetic counseling and testing 1, 3

Third-Trimester Surveillance Protocol

Growth Monitoring

Schedule a third-trimester ultrasound examination at 32-36 weeks to evaluate fetal growth, as isolated SUA is associated with increased risk of fetal growth restriction (FGR) with an adjusted odds ratio of 2.1 1, 2, 4

The evidence on FGR risk is somewhat conflicting:

• Some studies demonstrate increased FGR risk even after excluding fetuses with known anomalies 1, 4
• Other cohort studies found the observed incidence of FGR was not higher than expected 1
• However, large control studies demonstrate increased risk of FGR, polyhydramnios, oligohydramnios, placental abruption, cord prolapse, and perinatal mortality 1

Antenatal Fetal Surveillance

Begin weekly antenatal fetal surveillance at 36 0/7 weeks of gestation due to the nearly 5-fold increased risk of stillbirth (OR 4.80; 95% CI 2.67-8.62) 1, 2, 3

This recommendation is based on:

• Population-based case-control studies showing significantly increased stillbirth risk 1
• Increased risks of multiple pregnancy complications including placental abruption and cord prolapse 1, 2

Management if Growth Restriction Develops

If FGR is diagnosed during third-trimester surveillance:

Serial Doppler Assessment

• Perform serial umbilical artery Doppler assessment to monitor for deterioration 5
• Weekly umbilical artery Doppler when decreased end-diastolic velocity or severe FGR is present 5
• Increase to Doppler assessment 2-3 times weekly when absent end-diastolic velocity (AEDV) is detected due to potential for rapid deterioration 5

Delivery Timing Based on Doppler Findings

• Normal umbilical artery Doppler with estimated fetal weight 3rd-10th percentile: deliver at 38-39 weeks 5
• Decreased diastolic flow without AEDV/REDV, or severe FGR (estimated fetal weight <3rd percentile): deliver at 37 weeks 5
• Absent end-diastolic velocity: deliver at 33-34 weeks 5
• Reversed end-diastolic velocity (REDV): deliver at 30-32 weeks 5

Hospitalization Criteria

• Hospitalize if REDV is detected, administer antenatal corticosteroids, and perform cardiotocography at least 1-2 times daily 5
• Consider hospitalization if fetal surveillance more than 3 times per week is deemed necessary 5

Postnatal Considerations

Notify the pediatric provider of the prenatal SUA findings at the time of delivery, as postnatal examination reveals structural anomalies in up to 7% of infants with prenatal diagnosis of isolated SUA 1, 2, 6

This is critical because:

• Even when SUA appears isolated on prenatal ultrasound, approximately 7% of neonates prove to have structural anomalies at birth 1, 6
• Cardiac defects are the most common postnatal finding 6
• Gastrointestinal and central nervous system anomalies also occur with increased frequency 6

Common Pitfalls to Avoid

• Do not offer termination of pregnancy for isolated SUA—this is completely inappropriate for an isolated finding with no structural or chromosomal abnormalities 2
• Do not order unnecessary genetic testing for isolated SUA—it carries no increased aneuploidy risk and testing causes unnecessary anxiety 2
• Do not skip third-trimester growth assessment—even isolated SUA carries increased FGR risk that requires monitoring 1, 2
• Do not delay antenatal surveillance—the nearly 5-fold increased stillbirth risk necessitates weekly testing starting at 36 weeks 1, 2