Two-Vessel Cord (Single Umbilical Artery)
Medically reviewed by Dr. Lisa Okafor, MD, FACOG · Board-Certified OB-GYN
Content reviewed against published ACOG, NIH, March of Dimes guidelines
Last reviewed:
Your health matters just as much as your baby's. If you are dealing with two-vessel cord (single umbilical artery), here is what you need to know.
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.
Key takeaways
- 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.
- Usually normal when: Isolated SUA found at anatomy scan with all other structures normal
- Call your doctor if: Signs of growth restriction or decreased fetal movement
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What Parents Should Know
According to ACOG, NIH, March of Dimes guidelines, 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. At Second trimester, 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. It is generally considered normal when isolated SUA found at anatomy scan with all other structures normal. However, you should contact your pediatrician promptly if signs of growth restriction or decreased fetal movement.
Normal vs. Concerning
By Age
What to expect by age
Second trimester
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.
Third trimester
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 to Tell Your Pediatrician
- Describe when you first noticed two-vessel cord (single umbilical artery) and how it has changed over time.
- Note your baby's current age and which age-specific patterns you are seeing.
- Mention if you want to understand what SUA means for your baby.
- Mention if you are worried after hearing about the finding.
- Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
- Bring a list of any questions or observations you want to discuss at the appointment.
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
What You Can Do at Home
- Keep track of when you notice two-vessel cord (single umbilical artery) — noting the time of day, duration, and any triggers can help your pediatrician.
- Remember that isolated SUA found at anatomy scan with all other structures normal — this is generally within the range of normal.
- At Second trimester, focus on observation rather than intervention unless your pediatrician advises otherwise.
- Prioritize your own rest and nutrition. Accept help when offered, and do not hesitate to reach out to your healthcare provider.
- While monitoring at home, seek immediate care if signs of growth restriction or decreased fetal movement.
Related Conditions
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.
Related Resources
Frequently asked questions
Is two-vessel cord (single umbilical artery) normal?
When should I call the doctor about two-vessel cord (single umbilical artery)?
When is two-vessel cord (single umbilical artery) normal?
What causes two-vessel cord (single umbilical artery)?
What should I mention to my pediatrician about two-vessel cord (single umbilical artery)?
Is two-vessel cord (single umbilical artery) normal at Second trimester?
Is two-vessel cord (single umbilical artery) normal at Third trimester?
Should I go to the ER for two-vessel cord (single umbilical artery)?
Does two-vessel cord (single umbilical artery) go away on its own?
References
- [1]American College of Obstetricians and Gynecologists. Ultrasound During Pregnancy. ACOG, 2022. ACOG
- [2]National Library of Medicine. Single Umbilical Artery. StatPearls, 2023. NIH
- [3]March of Dimes. Umbilical Cord Conditions. March of Dimes, 2023. March of Dimes
Doctor Visit Checklist
Bring this checklist to your next pediatrician visit to discuss Two-Vessel Cord (Single Umbilical Artery).
Things to mention
- Describe when you first noticed two-vessel cord (single umbilical artery) and how it has changed over time.
- Note your baby's current age and which age-specific patterns you are seeing.
- Mention if you want to understand what SUA means for your baby.
- Mention if you are worried after hearing about the finding.
- Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
- Bring a list of any questions or observations you want to discuss at the appointment.
Observations to share
- 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
Urgent signs to report immediately
- Signs of growth restriction or decreased fetal movement
- Any typical pregnancy emergency signs
My notes
From ismybabyalright.com — free, evidence-based baby health guides
All content follows our editorial policy and is reviewed against published clinical guidelines.
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Related Resources
Bottom line
Most cases of two-vessel cord (single umbilical artery) are normal. Talk to your pediatrician if signs of growth restriction or decreased fetal movement.
Trust your instincts. If something feels wrong, reach out to your pediatrician. Worrying about your baby means you care — that is a good thing.
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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.