What is a Single Umbilical Artery?

Umbilical cord abnormalities can lead to serious detrimental health effects for a developing baby. In many cases, umbilical cord defects can lead to oxygen deprivation, neurological damage, or even stillbirth. Early intervention and treatment of these conditions are essential to protect the health of a developing baby.

What is the Umbilical Cord?

The umbilical cord is a flexible tube structure that connects the placenta to the fetus. In this regard, it carries important nutrients and blood from the placenta to a baby, which allows for normal, healthy development.

Typically, an umbilical cord has one vein and two arteries. The vein is responsible for carrying blood away from the baby back to the placenta. The arteries deliver plenty of oxygenated blood to the baby, which allows for the development of crucial organs.

In some pregnancies, the umbilical cord only has one artery, a condition called single umbilical artery (SUA). The phenomenon is a relatively common abnormality of pregnancy, occurring in about 1% of single pregnancies and as much as 5% of multiples. SUA may occur as the result of atrophy of an artery or the lack of initial development.

Babies with SUA can have an increased risk of complications and birth defects. The most common are small for gestational age and intrauterine growth restriction (IUGR). However, in some cases, an SUA does not affect an infant at all.

Diagnosing SUA

Pregnancy involves many tests designed to monitor both mother and her baby. The second-trimester ultrasound, which occurs between 17 and 20 weeks, provides a detailed look at a baby's anatomy, as well as the structures that support him or her. A technician takes pictures of the baby's vital organs, as well as the placenta and the umbilical cord. Using a tool called colored Doppler, the technician can also take recordings of the blood flow through the umbilical cord, so a doctor can assess if everything is working properly.

Health care providers most commonly diagnose SUA during this routine ultrasound. However, if there is adequate blood flow to the baby, SUA rarely leads to complications.

Management of SUA

Parents who hear that a baby has SUA may be concerned for his or her welfare. Any baby with a single umbilical artery merits careful monitoring to ensure that blood flow to the fetus remains adequate. Parents may also want to consider testing for birth defects or other malformations that might occur as the result of an SUA. The decision to pursue testing for these defects is optional and entirely up to the preferences of the parent. If a doctor decides that further testing is necessary for the health of the fetus, he or she may order amniocentesis, which is the removal of amniotic fluid from the uterus. A doctor can use this fluid to perform additional tests.

What is the Outlook for Babies With SUA?

The human body has an amazing ability to compensate. In many cases, the single umbilical artery will take on the functions of the missing one and a baby will continue to receive enough oxygen to thrive. Many moms with a single umbilical artery go on to have healthy, uneventful pregnancies.

Conservative measures for management, such as increased ultrasound and Doppler imaging through pregnancy and regular fetal monitoring during the third trimester, can help parents feel at ease. If SUA causes bradycardia (slow heart rate) from lack of oxygen, a provider will balance the risks of early delivery with those of lack of oxygen and deliver the baby as soon as possible via C-section. While rare, SUA can lead to complications like brain damage and cerebral palsy from lack of oxygen.