Single Umbilical Artery on Ultrasound: What Does a Two-Vessel Cord Mean?

The umbilical cord typically contains two arteries and one vein. However, in some pregnancies, ultrasound reveals only a single artery alongside the vein. This finding alone does not determine fetal health; therefore, the doctor reviews the rest of the anatomy, growth, and previous test results to decide if additional imaging or follow-up is needed, depending on whether the finding is isolated or accompanied by other observations.

• A single umbilical artery is an imaging finding that requires interpretation within the complete scan.
• Its presence as an isolated finding differs significantly from when other ultrasound markers are present.
• It does not, on its own, mean a genetic disorder, birth defect, or an inevitable cesarean delivery.
• The follow-up plan is determined by the physician based on the pregnancy status and test results.

What are a single umbilical artery and a two-vessel cord?

Normally, the umbilical cord consists of three blood vessels: one large vein that carries oxygen and nutrients from the placenta to the fetus and two smaller arteries that wrap around the vein to return waste and deoxygenated blood from the fetus back to the placenta. A single umbilical artery (SUA) condition, also known as a two-vessel cord, occurs when one of the two arteries is missing, leaving the cord with only one vein and one artery. This is a relatively common anatomical variation of the umbilical cord, and the fetal circulatory system usually adapts to compensate for the missing artery without significant issues.

How is it detected on ultrasound?

A single umbilical artery is typically detected during the detailed fetal anatomy scan, which is usually performed between weeks 18 and 22 of pregnancy. The sonographer or obstetrician uses ultrasound to take a cross-sectional view of the umbilical cord. Normally, the cross-section resembles a Mickey Mouse face, where the vein represents the head and the two arteries represent the ears. In a two-vessel cord, only two vessels are visible in the cross-section, and the doctor uses color Doppler to confirm active blood flow in just one artery alongside the vein.

Can the Ultrasound Result Be Uncertain?

Yes, sometimes the ultrasound result may not be entirely certain, especially if the scan is performed very early in pregnancy, if the fetal position inside the uterus prevents a clear view of the cord, or in cases of high maternal BMI, which can reduce ultrasound clarity. In such cases, the doctor may recommend repeating the scan after two to three weeks to obtain a better view and confirm the anatomical diagnosis accurately.

What is the Difference Between Isolated and Non-Isolated Cases?

This distinction is the most crucial step in evaluating the condition. When a single umbilical artery is detected, the doctor carefully looks for any other signs or anomalies in the fetal organs. If no other issues are found, the condition is called an "isolated single umbilical artery" (Isolated SUA), and in this case, the prognosis is excellent for delivering a completely healthy baby. However, if the condition is accompanied by other observations in organ development or anatomy, it is classified as "non-isolated" and requires deeper evaluation.

Does a Single Artery Mean a Genetic Problem?

The discovery of a single umbilical artery does not automatically mean there is a genetic problem or chromosomal syndrome in the fetus. In the vast majority of isolated cases, babies are born completely healthy and without any chromosomal abnormalities. However, clinical studies indicate that non-isolated cases (accompanied by other anatomical defects on ultrasound) may sometimes be associated with certain genetic syndromes such as Down syndrome or Edwards syndrome. Therefore, any link to genetic disorders depends on a comprehensive evaluation of the fetus, not on the cord finding alone.

What Tests Might the Doctor Discuss After Detection?

After detecting a single umbilical artery, your doctor may discuss some medical options to ensure pregnancy safety. These options include reviewing the results of early blood screening or non-invasive prenatal testing (NIPT) performed in the first trimester to check genetic health. In cases where other markers appear on ultrasound, the doctor may suggest consulting a specialist in high-risk pregnancy or maternal-fetal medicine to discuss more precise diagnostic tests like amniocentesis, though these are not routinely required for isolated cases.

How Are Fetal Organs and Growth Monitored?

Medical follow-up in the second and third trimesters focuses on monitoring fetal growth continuously to ensure the baby is gaining weight at a normal rate. Since the umbilical cord contains only two vessels instead of three, the medical team wants to ensure the placenta is functioning highly efficiently and the fetus is receiving adequate nutrients. This involves periodic ultrasounds to measure fetal dimensions, estimate weight, and compare them against standard growth charts.

Do I Need a Doppler or Repeated Growth Ultrasounds?

Yes, it is very common for doctors to recommend performing umbilical cord Doppler and growth ultrasounds repeatedly (e.g., every 3 to 4 weeks) during the third trimester. The Doppler scan helps measure blood flow resistance within the single umbilical artery, providing the medical team with a direct and accurate indicator of how easily blood and oxygen are reaching the fetus, ensuring early intervention if any decline in nutritional flow is detected.

Does it Affect the Timing or Method of Delivery?

In isolated single umbilical artery cases where fetal growth is normal and Doppler results are excellent, there is no medical reason to change the delivery timing or resort to an inevitable cesarean section. The mother can safely undergo vaginal delivery at full term. However, if monitoring reveals a decline in fetal growth or affected blood flow on Doppler, the medical team may decide to induce labor slightly early to protect the baby. The delivery method always depends on the overall health of the mother and baby, placental location, and fetal presentation.

When Should I Go to the Hospital Urgently?

Although single umbilical artery cases usually progress safely, pregnant women should always monitor general warning signs and go to the hospital immediately in case of a noticeable decrease in fetal movement, vaginal bleeding, fluid leakage (rupture of membranes), or regular, painful uterine contractions before the due date.

Medical Services Associated with Case Follow-up

• Detailed Fetal Anatomy Scan: Suitable for pregnant women at 18-22 weeks; involves a precise scan of all fetal organs to rule out associated anatomical defects, with the limitation that it depends on fetal position and does not guarantee 100% detection of all subtle anomalies.
• Maternal-Fetal Medicine Consultation: Suitable for cases where the single umbilical artery is accompanied by other findings; includes a comprehensive evaluation of high-risk pregnancy and establishing a customized follow-up plan, with the limitation of providing specialized medical advice without guaranteeing complete prevention of complications.
• Fetal Growth Ultrasound and Doppler: Suitable for pregnant women in the third trimester; includes measuring fetal weight and blood flow in the umbilical cord, with the limitation that it provides a snapshot of the current fetal status and requires periodic repetition as directed by the physician.