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

A single umbilical artery (SUA), also called a two-vessel cord, means the umbilical cord has one artery and one vein instead of the usual two arteries and one vein. It is found in about 1 in 100 pregnancies. In most cases it is the only finding, and an NHS leaflet states that a single umbilical artery can support a pregnancy and in most cases is not a cause for concern.

The cord links the baby to the placenta. The vein carries oxygen and nutrients to the baby, and the arteries carry blood and waste products back to the placenta. This guide explains what the finding usually leads to and what to ask. It cannot interpret your own scan.

A two-vessel cord does not cause symptoms, but the usual pregnancy warning signs still apply. The NHS advises calling emergency services if you are pregnant and bleeding and the bleeding is heavy (soaking a pad soon after putting it on), or you have severe tummy pain, shoulder pain, or you feel faint, dizzy or lose consciousness.

If your baby is moving less than usual, you cannot feel movements, or the pattern changes, the NHS says to call your midwife or maternity unit immediately, even in the middle of the night. Do not wait for your next growth scan, and do not use a home heartbeat monitor to reassure yourself.

Seek urgent advice too for a severe headache that does not ease, vision problems such as blurring or flashing lights, pain below the ribs, or sudden swelling of the face, hands or feet, which can be signs of pre-eclampsia.

Cleveland Clinic notes that scientists do not know exactly what causes a single umbilical artery. One artery may close, waste away or never form during early development.

Factors linked with a higher chance of SUA include carrying twins or more, having diabetes before pregnancy and the cord attaching to the placenta in an unusual position. Many people with a two-vessel cord have none of these.

Yes. ISUOG, the international society for ultrasound in obstetrics and gynaecology, states that in most cases SUA is an isolated finding. 'Isolated' means the single artery is the only difference seen on a detailed scan. 'Non-isolated' means there are other findings as well, for example in the baby's heart or kidneys.

The distinction matters because the outlook and next steps differ. ISUOG reports that there are no concerns after birth in isolated cases where babies are well grown. When there are other findings, the outlook depends on what those findings turn out to be; Cleveland Clinic reports chromosomal conditions in about 10% of non-isolated cases. Your care team will explain which group your scan falls into.

The first step is usually to confirm whether the single artery is isolated. ISUOG advises a detailed ultrasound to look for possible structural differences, particularly in the heart and kidneys. The routine mid-pregnancy scan, usually between 18 and 21 weeks, already checks for a set of conditions, but a more focused look may be arranged after SUA is seen.

Cleveland Clinic says a provider may also discuss a blood test to screen for genetic conditions. Any further tests depend on what the detailed scan shows. If the images are unclear, a repeat scan may be offered.

No ultrasound can find every condition. Ask your team what was checked and whether any views need repeating.

A two-vessel cord can sometimes increase the chance of the baby not growing as well as expected. Cleveland Clinic lists a higher chance of growth restriction, lower birth weight and preterm birth even in isolated cases, while noting that most babies with SUA have completely normal pregnancies with extra ultrasounds.

For this reason, extra growth scans are usually recommended later in pregnancy. As one example, an NHS trust leaflet describes offering a uterine artery Doppler scan at around 23 weeks, with growth scans then starting from 28 or 32 weeks and repeating every 2 to 4 weeks. Schedules vary between hospitals, so ask what your own plan is.

Growth scans measure the baby and help the team decide whether anything about care or timing of birth needs to change. Many people with SUA go on to have a typical birth.

For a baby with an isolated two-vessel cord who has grown well, ISUOG states there are no concerns after birth. If other findings were seen during pregnancy, the plan after birth depends on what those findings were, and your team will explain whether any checks of the baby are arranged.

Some parents worry about a future pregnancy. ISUOG estimates that the chance of SUA happening again roughly doubles after an isolated case, and is higher when other findings were present. Because SUA is uncommon to begin with, ask your team what this means for you and whether any extra scans would be offered next time.

Keep a copy of your scan reports. They can be useful if you move hospitals, see a new team or plan another pregnancy.

Bring your scan report and any earlier screening results. These questions can help you understand the plan.

• Is the single umbilical artery isolated, or were other findings seen?
• Were the baby's heart and kidneys looked at in detail, and were the views clear?
• Is any genetic screening or further testing being offered, and what would it add?
• When will growth scans start, how often will they be, and who will review them?
• Does this change where or how my baby should be born?
• Is anything planned for my baby after birth?
• Who do I contact if my baby's movements change or I have other concerns?

On SameCase, patients and verified doctors share de-identified cases. Reading how others with a two-vessel cord were followed with detailed scans and growth scans can help you think of questions to bring to your appointments.

Other people's experiences cannot predict what will happen in your pregnancy, and we do not offer a diagnosis. Your care team, who know your scan findings and history, are the right people to interpret them.