In a pregnancy with a single umbilical artery (SUA) identified, what is the risk of stillbirth and what antenatal surveillance and delivery timing are recommended?

Stillbirth Risk and Management in Single Umbilical Artery

Pregnancies with single umbilical artery (SUA) carry a nearly 5-fold increased risk of stillbirth (OR 4.80; 95% CI 2.67-8.62), mandating weekly antenatal fetal surveillance beginning at 36 weeks gestation and third-trimester growth ultrasound. 1

Stillbirth Risk Quantification

The stillbirth risk in SUA is substantially elevated compared to normal cord anatomy:

• Isolated SUA increases stillbirth odds by approximately 5-fold (OR 4.80; 95% CI 2.67-8.62) in population-based studies 1, 2, 3
• This elevated risk persists even when no other structural abnormalities are identified 1
• Additional risks include fetal growth restriction, oligohydramnios, placental abruption, cord prolapse, and perinatal mortality 1, 2

Initial Evaluation When SUA is Identified

When SUA is detected on prenatal ultrasound, perform the following assessment:

• Comprehensive anatomic survey with particular attention to cardiovascular and renal systems, as these are the most commonly affected organ systems 1, 3
• Cardiovascular anomalies show odds ratios ranging from 5.9 to 20.3 for various cardiac defects 3, 4
• Renal anomalies demonstrate a 3-fold increased risk, occurring in approximately 16% of isolated SUA cases 3, 4
• If adequate cardiac views are visualized and normal on the anatomy scan, dedicated fetal echocardiography is not routinely required 1, 2

Aneuploidy Risk Assessment

• For isolated SUA (no other structural abnormalities), no additional aneuploidy testing is recommended, regardless of whether previous screening was performed or declined 1, 2
• Isolated SUA carries no increased risk of chromosomal abnormalities 1, 2, 3
• When SUA occurs with other structural abnormalities (non-isolated SUA), aneuploidy risk ranges from 4% to 50% and genetic testing should be offered 1, 3

Antenatal Surveillance Protocol for Isolated SUA

Third-Trimester Growth Monitoring

• Schedule third-trimester ultrasound examination at 32-36 weeks to evaluate fetal growth 1, 2
• Isolated SUA is associated with a 2.1-fold increased risk of fetal growth restriction (adjusted OR 2.1; 95% CI 1.6-2.7) 2, 4
• This growth restriction risk persists even after excluding all fetuses with known anomalies 4

Fetal Surveillance Timing

• Initiate weekly antenatal fetal surveillance (non-stress testing or biophysical profile) beginning at 36 0/7 weeks gestation 1, 2
• This surveillance is warranted specifically due to the nearly 5-fold increased stillbirth risk 1, 2

Management When Fetal Growth Restriction Develops

If growth restriction is diagnosed during surveillance, escalate management according to umbilical artery Doppler findings:

Serial Doppler Assessment

• Perform serial umbilical artery Doppler assessment to monitor for deterioration when FGR is identified 5, 1
• With decreased end-diastolic velocity (flow ratios >95th percentile) or severe FGR (EFW <3rd percentile): weekly umbilical artery Doppler evaluation 5, 1
• With absent end-diastolic velocity: Doppler assessment 2-3 times per week 5, 1
• With reversed end-diastolic velocity: hospitalization, antenatal corticosteroids, and cardiotocography at least 1-2 times daily 5, 1

Cardiotocography Frequency

• Weekly cardiotocography testing after viability for FGR without absent/reversed end-diastolic velocity 5, 1
• Increase frequency when FGR is complicated by absent/reversed end-diastolic velocity or other comorbidities 5, 1

Delivery Timing Recommendations

Delivery timing is dictated by the presence and severity of fetal growth restriction and Doppler findings:

Isolated SUA Without Growth Restriction

• Standard obstetric management for timing of delivery (expectant management to 39-40 weeks) 1

With Fetal Growth Restriction

• EFW 3rd-10th percentile with normal umbilical artery Doppler: Deliver at 38-39 weeks 5, 1
• Decreased diastolic flow without absent/reversed end-diastolic velocity OR severe FGR (EFW <3rd percentile): Deliver at 37 weeks 5, 1
• Absent end-diastolic velocity: Deliver at 33-34 weeks 5, 1
• Reversed end-diastolic velocity: Deliver at 30-32 weeks 5, 1

Mode of Delivery

• Consider cesarean delivery for pregnancies with FGR complicated by absent/reversed end-diastolic velocity based on the complete clinical picture 5, 1
• Antenatal corticosteroids are indicated if delivery is anticipated before 33 6/7 weeks, or between 34 0/7 and 36 6/7 weeks in women at risk of delivery within 7 days 5, 1
• Intrapartum magnesium sulfate for neuroprotection is recommended for pregnancies <32 weeks 5, 1

Postnatal Considerations

• Notify the pediatric care team of the prenatal SUA finding at delivery 1, 2
• Postnatal examination is critical, as structural anomalies are revealed in up to 7% of infants with a prenatal diagnosis of isolated SUA 1, 2
• Cardiac defects represent the most common postnatal anomaly in this population 2

Critical Pitfalls to Avoid

• Do not omit third-trimester growth assessment, as isolated SUA carries a measurable 2.1-fold increase in FGR risk 2, 4
• Do not delay weekly antenatal surveillance after 36 weeks, given the near-5-fold rise in stillbirth risk 1, 2
• Do not order unnecessary genetic testing for isolated SUA, as it carries no increased aneuploidy risk and wastes resources while causing unnecessary anxiety 2
• Do not offer pregnancy termination for isolated SUA, as this is inappropriate for an isolated finding without structural or chromosomal abnormalities 2