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Single umbilical artery (SUA) is the most common umbilical cord anomaly, characterized by the absence of one of the two umbilical arteries, resulting in a two-vessel cord (one artery and one vein) instead of the normal three vessels.
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It may occur in isolation or be associated with structural anomalies or chromosomal abnormalities.
Normal anatomy:
| Structure | Normal |
|---|---|
| Umbilical cord | 2 arteries (carry deoxygenated blood from fetus) and 1 vein (oxygenated blood to fetus) |
| Embryologic basis | Formed from the allantoic and vitelline vessels; one artery may regress abnormally leading to SUA |
| Feature | Value |
|---|---|
| Incidence | ~0.5–1% of singleton pregnancies; up to 5% in twins |
| Laterality | Left-sided artery usually persists when one regresses |
| Detection | Increasingly diagnosed via prenatal ultrasound in 2nd trimester |
| Cause | Details |
|---|---|
| Primary agenesis | Failure to form second artery |
| Secondary atrophy | Involution or thrombosis of one artery |
| Risk factors | • Multiple gestation |
| • Diabetes mellitus | |
| • Advanced maternal age | |
| • Assisted reproductive techniques (IVF) |
| Modality | Findings |
|---|---|
| Axial view at fetal bladder | Normally shows 2 arteries coursing around the bladder; SUA = only one visible |
| Color Doppler | Confirms presence of only one artery adjacent to the bladder |
| Cord cross-section | Shows 2-vessel cord: 1 artery + 1 vein |
Sensitivity improves with color Doppler and proper technique at the level of the bladder.
Isolated SUA
| Outcome | Risk |
|---|---|
| Fetal growth | Mild risk of IUGR (~10–15%) |
| Perinatal outcome | Usually favorable if no associated anomalies |
| Management | Close fetal growth surveillance |