Two-Vessel Cord (Single Umbilical Artery)
The short answer
A single umbilical artery (SUA), also called a two-vessel cord, occurs when the umbilical cord has one artery instead of the typical two. It is found in about 1% of pregnancies. An isolated SUA (with no other abnormalities) is usually not a cause for concern, and most babies with an isolated SUA are born healthy.
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By Age
What to expect by age
SUA is typically discovered at the anatomy scan. If no other abnormalities are found (isolated SUA), the outlook is excellent. Your provider may recommend a follow-up growth ultrasound in the third trimester, as there is a small increased risk of the baby being smaller than expected. A detailed anatomy scan may be performed to rule out associated conditions.
Growth monitoring via ultrasound may be recommended. Most babies with isolated SUA grow normally and do not need any special care at delivery. If the SUA is associated with other findings, additional monitoring may be warranted.
What Should You Do?
When to take action
- Isolated SUA found at anatomy scan with all other structures normal
- Baby growing appropriately on follow-up ultrasound
- You want to understand what SUA means for your baby
- You are worried after hearing about the finding
- SUA was found alongside other ultrasound findings
- Signs of growth restriction or decreased fetal movement
- Any typical pregnancy emergency signs
Sources
Related Resources
Trust your instincts. If something feels wrong, reach out to your pediatrician.
Worrying about your baby means you care. That is a good thing.
Related Maternal Concerns
Soft Markers on Ultrasound
Soft markers are minor ultrasound findings that are usually variants of normal but may slightly increase the statistical risk of chromosomal conditions. Common soft markers include echogenic intracardiac focus (bright spot on heart), choroid plexus cysts (small cysts in the brain), and mild pyelectasis (slightly dilated kidneys). An isolated soft marker (one finding with no other concerns) is usually not significant.
Marginal Cord Insertion Concern
Marginal cord insertion occurs when the umbilical cord attaches at or near the edge of the placenta rather than centrally. It is found in about 7% of pregnancies. In most cases, it does not cause problems. Your provider may recommend growth monitoring to ensure the baby is receiving adequate nutrition, as marginal insertion can occasionally affect nutrient transfer.
20-Week Anatomy Scan Unexpected Findings
The 20-week anatomy scan checks your baby's major organs, structures, and growth. Most scans are completely normal. When unexpected findings are identified, they range from minor variants that resolve on their own to conditions that need further evaluation. Many findings require nothing more than a follow-up ultrasound to confirm the baby is developing well.
Dealing with Abnormal Prenatal Screening Results
An abnormal prenatal screening result can be terrifying, but it is important to understand that screening tests are designed to cast a wide net and have significant false-positive rates. Most people with abnormal screening results go on to have healthy babies after further testing confirms the baby is fine. An abnormal screening is a reason for more information, not a diagnosis.
Pregnancy Over 35 (Advanced Maternal Age)
While pregnancy after 35 carries some increased risks (including chromosomal abnormalities, gestational diabetes, and hypertension), the vast majority of people over 35 have healthy pregnancies and healthy babies. The term "geriatric pregnancy" is outdated and does not reflect reality. With appropriate prenatal care and monitoring, outcomes are excellent.
Amniocentesis Questions and Fears
Amniocentesis is a diagnostic test performed between 15-20 weeks that analyzes amniotic fluid to detect chromosomal conditions and genetic disorders with over 99% accuracy. The risk of pregnancy loss from the procedure is approximately 1 in 500-1,000 when performed by an experienced provider. Understanding the actual risks can help you make an informed decision.