Pregnancy Bliss | Reproductive Health Answers
Single umbilical artery (SUA)
There are normally three vessels in an umbilical cord: Two arteries and one vein. However, 1 in 100 babies are born with one umbilical arteries instead of two. With detailed ultrasound scan in mid-trimester, this anomaly is detected well before birth. Bearing in mind that this is so common, it goes without saying that the vast majority of these babies will be perfectly healthy. However, since it is a departure from the norm, the finding of a single umbilical artery does trigger a search for any other anomaly, especially that of the cardiovascular system. If a clear 4 chamber view of the heart is obtained and is normal, a fetal echocardiogram is not usually required.
However, the most important immediate concern once a single umbilical artery has been identified is the possibility of aneuploidy (chromosomal disorder). Whilst for all babies the incidence of SUA is 1%, the rate is almost 10 times that for babies with any of the known chromosomal disorders such as Down’s syndrome. It is therefore important to do a careful ultrasound examination looking specifically for structural anomalies and other soft markers associated with these conditions. If any of these is found, the mother should be offered a diagnostic test.
Besides the issue of chromosomal disorders, single umbilical artery (SUA) has been associated with intrauterine growth restriction (IUGR). It behoves the caregivers therefore to ensure growth of the baby is monitored throughout the pregnancy, if necessary by serial ultrasound scans especially after 28 weeks (third trimester).
Multiple soft markers
We have looked at each marker in isolation to examine their individual importance. However, you will have noticed that the recurring theme in all is that when another marker is found alongside any of them, the risk of a chromosomal disorder becomes much higher. The finding of a cluster of these soft markers is therefore regarded as a significant finding which should be actively investigated. Diagnostic tests should be encouraged unless parents do not wish to have these. Likewise, a combination of a soft marker and a structural abnormality (as listed above) carries the same degree of increased risk. One particular study showed that with two or more soft markers, the risk of an aneuploidy (chromosomal disorder) is increased 12-fold.
Last update: January 22, 2011
On the left picture, is a circled cross-section of a normal umbilical cord. Clearly visible is the large-bore umbilical vein and two smaller bore vessels which are the umbilical arteries. The picture on the right shows the vessel with only one artery. Approximately 1% of all babies are found to have a single umbilical artery in their cords.