Typically, an umbilical cord has two arteries and one vein. However, some babies have just one artery and vein. This condition is known as a two-vessel cord diagnosis.
Doctors also call this a single umbilical artery (SUA). According to Kaiser Permanente, an estimated 1 percent of pregnancies have a two-vessel cord.
The umbilical cord is responsible for transporting oxygen-rich blood to a baby and taking away oxygen-poor blood and waste products from a baby.
The umbilical vein carries oxygen-rich blood to the baby. The umbilical arteries carry oxygen-poor blood away from the fetus and to the placenta. The placenta then returns the wastes to the mother’s blood, and the kidneys eliminate them.
Several umbilical cord abnormalities exist, including an umbilical cord that’s too short or long. Another is a two-vessel cord or SUA. This cord type has a single artery and vein instead of two arteries and a vein.
Doctors don’t know exactly what causes a two-vessel cord to develop. One theory is that an artery doesn’t grow properly in the womb. Another is that the artery doesn’t divide in two as it normally would.
Some women are more likely to have a two-vessel cord than others. Risk factors for a two-vessel cord include:
- being a white person
- being older than age 40
- being pregnant with a girl
- having a history of diabetes or high blood sugar episodes during pregnancy
- pregnant with multiple babies, like twins or triplets
- taking medications known to affect fetal growth, like phenytoin
However, these risk factors don’t guarantee a mother will have a baby that has a two-vessel cord.
Doctors usually identify a two-vessel cord during a prenatal ultrasound. This is an imaging study of the baby.
Doctors typically look for the umbilical arteries in the second trimester exam at around 18 weeks. However, sometimes the position of a baby makes it hard for your doctor to fully view the cord.
Another option is a color-flow Doppler ultrasound machine, which can help a doctor detect a two-vessel cord earlier. This is usually around 14 weeks’ gestation. If you are worried about your baby’s risk for a two-vessel cord, talk to your doctor.
For some women, a two-vessel cord diagnosis doesn’t cause any noticeable differences in their pregnancies. There are many babies that have a single umbilical artery that have healthy pregnancies and deliveries.
However, some babies with a single artery are at increased risk for birth defects. Examples of birth defects that babies with a two-vessel diagnosis may have include:
- heart problems
- kidney problems
- spinal defects
A two-vessel cord is also associated with a greater risk for the genetic abnormality known as VATER. This stands for vertebral defects, anal atresia, transesophageal fistula with esophageal atresia, and radial dysplasia.
Babies with a two-vessel cord may also be at higher risk for not growing properly. This could include preterm delivery, slower-than-normal fetal growth, or stillbirth. Your doctor can discuss these individual risks with you.
Doctors can often see many of the complications a baby can experience due to a two-vessel cord on a high-resolution ultrasound.
If your doctor or ultrasound technician detects a two-vessel cord by lower definition ultrasound, they may suggest a higher resolution scan to more closely examine your baby’s anatomy. Sometimes your doctor may also recommend amniocentesis. This test can help determine lung maturity and other development-related conditions.
Other tests or reviews a doctor may recommend include:
- personal medical history
- family medical history
- fetal echocardiogram (viewing the chambers and workings of the fetal heart)
- screening for genetic abnormalities in pregnancy, like an aneuploidy screening
If your baby doesn’t appear to have any adverse effects from a two-vessel cord, this is known as an isolated single umbilical artery (SUA).
If your doctor doesn’t suspect that your baby is experiencing any adverse side effects from a two-vessel cord diagnosis, they may recommend an ultrasound in the future. This could include on a monthly basis or simply in your third trimester, to ensure your baby is growing proportionally for their age. Even if a doctor has called your two-vessel cord an isolated SUA, there’s still a risk for slower than normal fetal growth. This is known as intrauterine growth restriction (IUGR).
Having a two-vessel cord isn’t associated with greater risk for C-section versus vaginal delivery. However, if your baby does have some organ dysfunction, they may need to receive care in the neonatal intensive care unit (NICU) after birth.
If your doctor has diagnosed your baby with having a two-vessel cord, more testing is likely required.
While some babies have no complications as a side effect of a two-vessel cord, some can. A doctor and possibly a genetic specialist can help determine the next steps and diagnosis with you and your partner.