How should an isolated single umbilical artery detected on prenatal ultrasound be managed to reduce the risk of stillbirth and growth restriction?

Management of Isolated Single Umbilical Artery to Reduce Stillbirth and Growth Restriction Risk

For an isolated single umbilical artery detected on prenatal ultrasound, implement a two-phase surveillance protocol: perform a third-trimester growth ultrasound at 32-36 weeks, followed by weekly antenatal fetal surveillance beginning at 36 weeks gestation to mitigate the nearly 5-fold increased risk of stillbirth. 1

Initial Assessment When SUA Is Detected

When a single umbilical artery is identified on prenatal ultrasound, your immediate priority is to determine whether it is truly isolated:

• Perform a comprehensive cardiac and renal anatomic assessment on the same anatomy scan, as cardiovascular and renal systems are the most commonly affected when SUA occurs with structural abnormalities 1
• If the routine anatomy scan provides adequate cardiac views that are normal, do not order a dedicated fetal echocardiogram—it is not routinely warranted for isolated SUA 1
• Do not order additional aneuploidy testing regardless of whether previous screening was performed or what those results showed, as isolated SUA carries no increased risk of chromosomal abnormalities 1

Common Pitfall to Avoid

The distinction between isolated and non-isolated SUA is critical. When SUA occurs with other structural abnormalities, the aneuploidy risk ranges from 4% to 50% 2, but isolated SUA has no increased aneuploidy risk 1. Do not waste resources on unnecessary genetic testing for truly isolated cases 1.

Third-Trimester Growth Surveillance

The cornerstone of management for isolated SUA is enhanced growth monitoring:

• Schedule a third-trimester ultrasound between 32-36 weeks to assess fetal growth, as isolated SUA is associated with a 2.1-fold increased risk of fetal growth restriction 1
• This single third-trimester assessment is adequate for isolated cases without evidence of growth restriction 1

Evidence Nuance on Serial Growth Assessments

There is some conflicting evidence regarding the frequency of growth assessments. One study found only a 2.9% incidence of growth restriction with serial assessments 3, while a larger cohort study demonstrated a significant association (adjusted OR 2.1) even after excluding fetuses with anomalies 4. The guideline recommendation of a single third-trimester assessment represents a balanced approach 1, though if growth restriction is identified, serial assessments at 3-4 week intervals become appropriate 2.

Antenatal Fetal Surveillance Protocol

Begin weekly antenatal fetal surveillance at 36 0/7 weeks gestation for all pregnancies with isolated SUA 1. This recommendation is based on the substantial stillbirth risk:

• Isolated SUA confers an approximately 5-fold increased risk of stillbirth (OR 4.80; 95% CI 2.67-8.62) 1
• Additional risks include polyhydramnios, oligohydramnios, placental abruption, cord prolapse, and perinatal mortality 1

Surveillance Intensity Based on Growth Status

If fetal growth restriction is not identified:

• Continue weekly antenatal surveillance from 36 weeks until delivery 1
• Standard obstetric management for timing of delivery applies 2

If fetal growth restriction is diagnosed:

• Initiate weekly umbilical artery Doppler assessment to monitor for deterioration 2
• Begin weekly cardiotocography testing after viability 2
• Increase surveillance frequency based on Doppler findings (see below) 2

Management Algorithm When Growth Restriction Develops

If growth restriction is identified during third-trimester surveillance, your management escalates based on umbilical artery Doppler findings:

Normal Doppler with EFW 3rd-10th Percentile

• Continue weekly umbilical artery Doppler 2
• Plan delivery at 38-39 weeks 2

Decreased Diastolic Flow (without absent/reversed end-diastolic velocity) OR Severe FGR (EFW <3rd percentile)

• Continue weekly umbilical artery Doppler 2
• Plan delivery at 37 weeks 2

Absent End-Diastolic Velocity (AEDV)

• Increase Doppler assessment to 2-3 times weekly due to potential for rapid deterioration 2
• Plan delivery at 33-34 weeks 2
• Consider cesarean delivery based on the complete clinical picture 2

Reversed End-Diastolic Velocity (REDV)

• Hospitalize immediately 2
• Administer antenatal corticosteroids 2
• Perform cardiotocography at least 1-2 times daily 2
• Plan delivery at 30-32 weeks 2
• Consider cesarean delivery based on the complete clinical picture 2

Hospitalization Criteria

Admit to the hospital if fetal surveillance more than 3 times per week is deemed necessary 2, which typically occurs with AEDV or REDV findings.

Postnatal Considerations

• Notify the pediatric care team of the prenatal SUA finding at the time of delivery 1
• Postnatal examination is essential because structural anomalies are revealed in up to 7% of infants who were prenatally classified as having isolated SUA 1
• Cardiac defects represent the most common postnatal anomaly in this group 5

Renal Imaging Controversy

Despite the 3-fold increased risk of renal anomalies associated with SUA 5, the largest series of isolated SUA found no excess of significant renal malformations (1.6%, similar to controls at 0.4%) 6. Routine postnatal renal ultrasonography is not warranted for truly isolated cases 6, though the pediatric team should maintain clinical vigilance.

Critical Pitfalls to Avoid

• Never offer pregnancy termination for isolated SUA—it is completely inappropriate for an isolated finding without structural or chromosomal abnormalities 1
• Do not order unnecessary genetic testing for isolated SUA, as it wastes resources and causes unnecessary anxiety when isolated SUA carries no increased aneuploidy risk 1
• Do not omit the third-trimester growth assessment—isolated SUA carries a measurable 2.1-fold increase in growth restriction risk 1
• Do not delay weekly antenatal surveillance after 36 weeks—the nearly 5-fold rise in stillbirth risk mandates this surveillance 1