Single Umbilical Artery: Clinical Implications and Management
Immediate Assessment
When a single umbilical artery (SUA) is identified, perform a comprehensive anatomic survey with particular attention to cardiovascular and renal systems, as these are the most commonly affected organ systems. 1, 2
Cardiac Evaluation
- A thorough cardiac assessment on the standard anatomy scan is adequate—fetal echocardiography is not routinely warranted if the cardiac anatomy appears normal on detailed anatomic survey. 1
- Cardiovascular anomalies show the strongest association with SUA, with odds ratios ranging from 5.9 to 20.3 for various cardiac defects. 2
- Up to 67% of fetuses with SUA may have associated structural anomalies, with cardiac defects being particularly common. 3
Renal Assessment
- Renal anomalies demonstrate a 3-fold increased risk, with approximately 16% of isolated SUA cases having some form of renal abnormality. 2
- Five of six fetuses with associated anomalies in one series had urinary system involvement. 4
Genetic Counseling and Testing
If aneuploidy screening (serum or cell-free DNA) was negative or not previously performed, no additional genetic testing is needed for isolated SUA. 5, 1
Key Distinctions
- Isolated SUA shows no increased risk of aneuploidy. 5, 2
- When SUA occurs with other structural abnormalities, the frequency of associated aneuploidy ranges from 4% to 50%. 2
- All karyotypically abnormal fetuses in one series had a structural defect in addition to the SUA. 3
Growth Monitoring Protocol
Perform a third-trimester ultrasound examination (typically around 32-36 weeks) to evaluate fetal growth. 5, 1, 2
Evidence on Growth Restriction
The evidence regarding growth restriction risk is somewhat conflicting:
- The Society for Maternal-Fetal Medicine and recent large cohort studies demonstrate an increased risk of intrauterine growth restriction (IUGR) with isolated SUA (adjusted OR 2.1,95% CI 1.6-2.7), even after excluding fetuses with known anomalies. 6
- One smaller longitudinal study found only 2.9% of isolated SUA pregnancies developed IUGR (EFW ≤10th percentile), suggesting the risk may not be substantially increased. 7
- However, another series showed 50% of fetuses with isolated SUA (no structural or chromosomal anomalies) demonstrated growth restriction. 3
Given the weight of evidence from the largest and most recent studies, serial growth assessment is reasonable and recommended by current guidelines. 5, 1, 6
Antenatal Surveillance
Consider weekly antenatal fetal surveillance (nonstress testing or biophysical profile) beginning at 36 weeks of gestation. 5, 1, 2
Rationale for Enhanced Surveillance
- SUA is associated with a nearly 5-fold increased risk of stillbirth (OR 4.80,95% CI 2.67-8.62). 2
- Additional risks include polyhydramnios, oligohydramnios, placental abruption, cord prolapse, and increased perinatal mortality. 1
- Neonates with isolated SUA weigh on average 320 grams less, are delivered 1 week earlier, and have lower Apgar scores compared to those with three-vessel cords. 8
Delivery Planning
No specific timing of delivery is indicated for isolated SUA—proceed with routine obstetric management unless growth restriction or other complications develop. 5, 1
- If IUGR develops in the context of SUA, follow standard FGR management protocols including Doppler assessment and timing of delivery based on severity. 9
Postnatal Considerations
Notify the pediatric team at delivery of the prenatal SUA diagnosis. 1
- Postnatal examination of infants with prenatal diagnosis of isolated SUA revealed structural anomalies in up to 7% of cases that were not detected prenatally. 1
- Clinical examination of the umbilical cord after delivery is important, as obstetricians and pediatricians fail to diagnose 24% and 16% of SUA cases respectively at delivery. 8
Common Pitfalls to Avoid
- Do not assume the side of the missing artery (right vs. left) has clinical significance—the selection process appears random, and no correlation exists between the side and type or severity of malformations. 4
- Do not order fetal echocardiography reflexively—a detailed cardiac assessment on the anatomy scan is sufficient if normal. 1
- Do not pursue amniocentesis for isolated SUA with negative aneuploidy screening—the risk is not increased in truly isolated cases. 5, 1