Single Umbilical Artery

Single umbilical artery (SUA) is the most common malformation of the umbilical cord. On its own, SUA does not necessarily pose a risk to you or your child as an umbilical cord with just one artery is sufficient to support a pregnancy to term. However, SUA does increase your child’s risk for certain birth defects.

What is Single Umbilical Artery?

Normally, when the umbilical cord develops, it forms three vessels: two arteries and one vein. However, in some cases, just one artery develops. Precisely why this occurs is not entirely known. It is suspected, though, that one artery may simply stop growing as it develops or perhaps that the primordial umbilical artery does not divide properly.

How Common is SUA?

This malformation of the umbilical cord has been found to affect between 0.5% and 7% of pregnancies and 1 in 100 live births. Caucasian women are twice as likely to experience this complication compared to Japanese and Black women. Additionally, women having a multiple pregnancy are three to four times as likely to develop SUA. Other factors that may increase your risk:

• Advanced maternal age (over 40)
• Having 3 or more previous children
• Diabetes
• Female fetal sex

Although SUA can affect either artery, the left artery tends to be absent slightly more often than the right.

How Will I Know if I have SUA?

Although some babies may not be diagnosed until birth, most times, the problem can be diagnosed through an ultrasound scan. During an ultrasound, an SUA diagnosis will be made if the technician notices that one artery is abnormally large and that only two vessels are visible instead of three.

Alternatively, a colour doppler ultrasound may also be done. In this instance, the colour doppler will be used to visualize the arteries. If you have single umbilical artery, then only one vessel will be seen on the screen on either side of your baby’s bladder.

SUA has Been Found; Will My Baby be Born Healthy?

Anywhere from half to two-thirds of babies born with single artery umbilical cord are born healthy and with no chromosomal or congenital abnormalities.

Of the remaining babies with SUA (single umbilical artery) , some studies suggest that about 25 percent have birth defects, including chromosomal and/or other abnormalities.

These can include trisomy 13 or trisomy 18. However, the most common pregnancy complications that occur in infants with SUA are heart defects, gastrointestinal tract abnormalities and problems with the central nervous system.

The respiratory system, urinary tract, and musculoskeletal system may also be affected. One in five babies affected by SUA will be born with multiple malformations.

Aside from these problems, between 15% and 20% of infants with SUA may suffer from intrauterine growth retardation. Single umbilical artery also has an increased miscarriage rate of 22% associated with it, likely due to the increased abnormalities. Furthermore, there is an association between SUA and low birthweight (<2500g) and early delivery (<37 weeks).

Will I Need Extra Screening if My Baby has SUA?

It is likely that you will receive a more thorough ultrasound scan in order to detect any abnormalities.

Since ultrasound scans are very good at picking up abnormalities, if you have a normal ultrasound, then it is likely that your baby will be born without any congenital or chromosomal abnormalities. A fetal echocardiogram may also be performed to check the health of your child.

In the presence of an otherwise reassuring prenatal ultrasound, the only other change to antenatal care one might make is a growth scan to make sure the baby is growing at a ‘normal’ rate toward the last month of pregnancy.