During a prenatal ultrasound, you may hear:
“Your baby has a two-vessel cord.”
That can sound worrying—especially if you were expecting the umbilical cord to have three vessels.
Normally, the umbilical cord contains:
two umbilical arteries + one umbilical vein.
When only one umbilical artery is identified, the finding is called a single umbilical artery (SUA).
It is also commonly called a:
two-vessel cord.
But what does that actually mean for your baby?
The answer depends largely on one important question:
Is the SUA isolated?
What Does a Normal Umbilical Cord Look Like?
A typical umbilical cord contains three blood vessels.
Two umbilical arteries
These carry blood from the fetus toward the placenta.
One umbilical vein
This carries oxygenated blood from the placenta back toward the fetus.
On ultrasound, these vessels can be evaluated in several ways.
One particularly useful view is around the fetal bladder, where the two umbilical arteries normally course along either side of it.
When only one artery is seen, SUA may be suspected.
What Is a Single Umbilical Artery?
A single umbilical artery means that the umbilical cord contains:
one artery + one vein
instead of the usual:
two arteries + one vein.
This is why you may also hear the term two-vessel cord.
Importantly, SUA does not mean that the baby has only two blood vessels in the entire body.
It specifically describes the vessels within the umbilical cord.
How Is SUA Found on Ultrasound?
Sometimes SUA is suspected when the umbilical cord itself is examined in cross-section.
A normal cord may show:
three vessel lumens.
With SUA, only:
two vessel lumens
are present.
But counting vessels in one image is not always enough.
Sonographers can also use color Doppler to examine the arteries around the fetal bladder.
Normally, two umbilical arteries are seen traveling along opposite sides of the bladder.
With SUA, only one is identified.
Looking at the vessels in more than one way helps confirm the finding.
Does SUA Hurt the Baby?
Not necessarily.
Many babies with an isolated SUA develop normally.
The remaining umbilical artery can usually continue carrying blood between the fetus and placenta.
So SUA does not automatically mean that the baby is not receiving enough blood or oxygen.
However, because SUA can sometimes occur together with other fetal abnormalities, the rest of the anatomy scan becomes especially important.
Why Does the Sonographer Look More Carefully After Finding SUA?
Once SUA is suspected, the examination does not stop at the cord.
The sonographer and physician will carefully evaluate the rest of the fetus.
Particular attention may be given to:
- the heart
- kidneys and urinary tract
- brain
- spine
- abdominal anatomy
- limbs
- fetal growth
- other structural findings
The purpose is to determine whether the SUA is truly isolated.
What Does “Isolated SUA” Mean?
An isolated SUA means that the single umbilical artery is found without another identified fetal structural abnormality or additional concerning ultrasound finding after appropriate evaluation.
This distinction matters.
Isolated SUA
SUA is the only significant finding.
Non-isolated SUA
SUA is present together with another fetal abnormality or concerning finding.
These situations may require very different counseling and evaluation.
Is SUA Associated With Chromosome Conditions?
SUA can occur in fetuses with chromosomal abnormalities, particularly when other structural abnormalities are also present.
But an SUA by itself is not a diagnosis of a chromosome condition.
This is another reason doctors interpret the finding together with:
the complete anatomy scan
and
previous prenatal screening results.
When SUA is isolated, the interpretation is considerably more reassuring than when multiple abnormalities are identified.
Do I Need Amniocentesis Because of SUA?
Not simply because an isolated SUA was found.
Current SMFM guidance states that for an isolated single umbilical artery, no additional evaluation for aneuploidy is recommended solely because of the SUA, regardless of whether previous aneuploidy screening was negative or had not been performed.
However, if other abnormalities are present, the situation changes and additional genetic counseling or diagnostic testing may be discussed.
So again:
SUA alone and SUA with additional abnormalities are not the same clinical picture.
Does SUA Mean My Baby Has a Heart Defect?
No.
SUA itself is an umbilical cord finding, not a congenital heart defect.
However, because cardiac abnormalities can sometimes occur alongside SUA, careful assessment of fetal cardiac anatomy is important during the detailed examination.
If the heart appears abnormal or adequate cardiac views cannot be obtained, additional evaluation may be recommended based on the overall findings.
What About the Kidneys?
The urinary tract also receives careful attention.
SUA has been associated with renal and urinary tract abnormalities in some fetuses.
That does not mean a baby with SUA automatically has a kidney problem.
It means the kidneys, renal pelvises, bladder, and surrounding anatomy should be assessed carefully as part of the complete fetal examination.
Can SUA Affect Fetal Growth?
This is another important part of follow-up.
Even when SUA appears isolated, pregnancies with SUA have been associated with an increased risk of fetal growth restriction compared with pregnancies with a three-vessel cord.
For this reason, fetal growth may be reassessed later in pregnancy.
SMFM recommends a third-trimester ultrasound to evaluate fetal growth for isolated SUA.
Will I Need More Ultrasounds?
Often, yes—at least for growth assessment.
If the anatomy scan is otherwise reassuring, a later ultrasound may evaluate:
- fetal growth
- estimated fetal weight
- amniotic fluid
- overall fetal well-being as clinically appropriate
If another abnormality is identified, the follow-up plan may be more extensive.
The exact schedule depends on the pregnancy and your healthcare provider’s recommendations.
Does SUA Mean the Placenta Is Not Working Properly?
Not automatically.
SUA describes the number of vessels in the umbilical cord.
It does not by itself diagnose placental insufficiency.
Most isolated SUA pregnancies do not simply progress to placental failure because one artery is absent.
Instead, clinicians monitor fetal growth because some pregnancies have a higher risk of growth problems.
This is an important distinction:
Monitoring for a risk is not the same as saying the complication will happen.
Will My Baby Need to Be Delivered Early?
Not simply because an isolated SUA is present.
Delivery timing depends on the entire pregnancy.
If:
fetal growth remains appropriate
fetal surveillance is reassuring
and
there are no other obstetric complications,
SUA alone does not automatically mean preterm delivery is necessary.
If fetal growth restriction or another complication develops, delivery planning may change accordingly.
Does SUA Mean I Need a C-Section?
No.
A two-vessel cord alone does not automatically require cesarean delivery.
The mode of delivery is determined by the usual obstetric considerations and any additional pregnancy complications.
Many pregnancies with isolated SUA can proceed toward vaginal delivery.
What Happens After Birth?
If SUA was isolated prenatally and the baby appears well, postnatal management depends on the prenatal findings, newborn examination, and local clinical practice.
The pediatric team should know that SUA was identified during pregnancy.
If prenatal imaging suggested a kidney, cardiac, or other abnormality, additional postnatal evaluation may be needed.
But the presence of SUA alone does not mean that every baby will require extensive testing after birth.
Questions to Ask Your Doctor
If SUA is found during your anatomy scan, useful questions include:
- Is the SUA isolated?
- Was the baby’s heart anatomy reassuring?
- Do both kidneys look normal?
- Was the rest of the anatomy scan normal?
- Were any other soft markers identified?
- Do my prenatal screening results change the interpretation?
- Do I need additional genetic testing?
- When should fetal growth be checked again?
- Does this change my delivery plan?
- Will my baby need any evaluation after birth?
And perhaps the most important question:
“Is this simply a two-vessel cord, or is anything else abnormal?”
That distinction often determines what happens next.
Key Takeaway
A single umbilical artery (SUA) means the umbilical cord contains:
one artery + one vein
instead of the usual:
two arteries + one vein.
It is commonly called a two-vessel cord.
SUA does not automatically mean that your baby has a chromosome condition, heart defect, kidney abnormality, or growth problem.
The most important step is determining whether it is isolated.
When the rest of the detailed anatomy scan is reassuring, the picture is generally much more favorable.
However, because isolated SUA is associated with an increased risk of fetal growth restriction, third-trimester growth assessment is commonly recommended.
So if you’re told:
“Your baby has a two-vessel cord,”
don’t stop at that sentence.
Ask:
“Is everything else developing normally?” 👶🩵
That’s the bigger picture.
About the Author
This article was written by a sonographer with over 20 years of hands-on clinical ultrasound experience, including fetal, breast, and thyroid imaging.
The umbilical cord may look like a small part of the examination, but its vessels provide important information. When SUA is identified, the goal of ultrasound is not simply to count the vessels—it is to carefully evaluate the baby as a whole and determine whether the finding is isolated.
This article is for general educational purposes and does not replace individualized prenatal diagnosis, genetic counseling, maternal-fetal medicine evaluation, or medical advice from your healthcare provider.
