What is the management and significance of a single umbilical artery (SUA) in pregnancy?

Management and Significance of Single Umbilical Artery in Pregnancy

When an isolated single umbilical artery (SUA) is identified, perform a comprehensive cardiac and renal anatomic assessment, obtain a third-trimester growth ultrasound, and initiate weekly antenatal surveillance beginning at 36 weeks of gestation. 1, 2

Clinical Significance and Associated Risks

Isolated SUA carries substantially increased risks for adverse perinatal outcomes despite the absence of other structural abnormalities. The condition is associated with:

• 5-fold increased risk of perinatal and intrauterine death (OR 5.62,95% CI 4.69-6.73) 3
• 73% increased risk of preterm birth 3
• 55% increased risk of small-for-gestational-age neonates 3
• Increased rates of stillbirth (OR 4.80,95% CI 2.67-8.62), oligohydramnios, placental abruption, cord prolapse, and perinatal mortality 2

These risks justify enhanced surveillance protocols even when SUA appears isolated. 1, 2, 3

Initial Diagnostic Workup

Anatomic Survey

• Perform detailed assessment of cardiovascular and renal systems, as these are the most commonly affected organ systems when SUA occurs with structural abnormalities 1, 2
• If cardiac views on the anatomy scan are adequately visualized and normal, fetal echocardiography is not routinely warranted 1, 2
• Vigilant search for associated anomalies is essential, as 67% of fetuses with SUA have associated structural anomalies 4

Genetic Considerations

• No additional genetic testing is needed for isolated SUA if aneuploidy screening was negative or low-risk, as isolated SUA shows no increased risk of aneuploidy 1, 2
• However, when SUA occurs with structural abnormalities, aneuploidy risk ranges from 4% to 50% 2
• SUA fetuses have 15.35 times greater risk of chromosomal abnormalities when other anomalies are present 5

Surveillance Protocol for Isolated SUA

Growth Monitoring

• Obtain third-trimester ultrasound examination to evaluate fetal growth, as neonates with isolated SUA have increased rates of growth restriction 1, 2
• Perform serial growth assessments at 3-4 week intervals (more reliable than 2-week intervals given inherent biometric error) 2
• Growth restriction occurs in approximately 50% of fetuses with truly isolated SUA 4

Antenatal Testing

• Initiate weekly antenatal fetal surveillance beginning at 36 weeks of gestation for fetuses with isolated SUA 1, 2
• This recommendation is based on the significantly increased risks of stillbirth, polyhydramnios, oligohydramnios, placental abruption, and cord prolapse 1

Important caveat: One older study from 2008 suggested serial growth assessments may not be indicated 6, but this contradicts current ACOG guidelines and more recent population-based evidence demonstrating clear increased risks 1, 2, 3. The guideline recommendations should take precedence.

Management When Growth Restriction Develops

Doppler Surveillance Intensity

If fetal growth restriction is diagnosed in the setting of SUA:

• Weekly umbilical artery Doppler evaluation when decreased end-diastolic velocity (flow ratios >95th percentile) or severe FGR (EFW <3rd percentile) is present 2
• Doppler assessment 2-3 times per week when absent end-diastolic velocity (AEDV) is detected due to potential for rapid deterioration 2
• Weekly cardiotocography (CTG) testing after viability, with increased frequency if complicated by AEDV/REDV or other comorbidities 2

Hospitalization Criteria

• In the setting of reversed end-diastolic velocity (REDV), hospitalize the patient, administer antenatal corticosteroids, and perform CTG at least 1-2 times daily 2
• Hospital admission should be considered if fetal surveillance more often than 3 times per week is deemed necessary 7

Timing of Delivery

For Isolated SUA Without Growth Restriction

• Standard obstetric management for timing of delivery 2

For SUA With Growth Restriction

The timing is dictated by umbilical artery Doppler findings:

• Normal umbilical artery Doppler with EFW 3rd-10th percentile: Deliver at 38-39 weeks 2
• Decreased diastolic flow without AEDV/REDV, or severe FGR (EFW <3rd percentile): Deliver at 37 weeks 2
• Absent end-diastolic velocity: Deliver at 33-34 weeks 2
• Reversed end-diastolic velocity: Deliver at 30-32 weeks 2

Third Stage of Labor Considerations

Pregnancies with isolated SUA carry increased risk of third stage complications:

• Increased risk of postpartum hemorrhage 3
• Increased need for manual placental removal or curettage 3
• Associated with small placenta, placenta previa and abruption, anomalous cord insertion, long cord, and cord knots 3, 5
• Preparedness for third stage complications is warranted 3

Postnatal Management

• Notify the pediatric provider of the prenatal findings at the time of delivery 1, 2
• Postnatal examination is critical, as structural anomalies have been revealed in up to 7% of infants with a prenatal diagnosis of isolated SUA 1, 2
• The most common congenital anomalies in chromosomally normal fetuses are genitourinary (6.48%), cardiovascular (6.25%), and musculoskeletal (5.44%) 5

Recurrence Risk

• Women with isolated SUA in one pregnancy carry increased risk of SUA in subsequent pregnancies 3
• This information is relevant for counseling regarding future pregnancies