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Single umbilical artery

Last revised by Dr Sandeep Singh Awal on 08 Dec 2021

Single umbilical artery (SUA) results when there is a congenital absence of either the right or left umbilical artery. In the usual situation, there are paired umbilical arteries. For unknown reasons, the absence of the left umbilical artery is much more common (~70%).

The estimated prevalence is ~0.4-1% of pregnancies 5,6,10. There may be an increased incidence of twin pregnancies and maternal diabetes.

The occurrence of a single umbilical artery is thought to be due to secondary atresia or atrophy rather than primary agenesis of the artery. The remaining single artery is often quite large and approaches the size of the umbilical vein (which is usually larger than the artery). 

In ~65% (range 57-75%) of cases, a single umbilical artery is present in isolation 1,2.

When found in isolation, it is usually not of clinical significance but there is an increased incidence of intrauterine growth restriction (IUGR) 6 (~15%). 

Recognized associations are thought to be present in ~35% (range 25-43%) of cases:

When found with other fetal anomalies, it can be also be associated with:

Some suggest that complex congenital and chromosomal abnormalities are found almost exclusively when the left umbilical artery is absent 9

This is the imaging investigation of choice and an SUA is often detected incidentally on ultrasound. High-resolution ultrasound has a sensitivity and specificity approaching 100% 1. Sonographic features include:

  • two vessels within the umbilical cord (one artery and one vein) instead of the usual three (best seen in cross-section)
  • the single artery is often larger in caliber than normal and approaches the diameter of the accompanying vein
  • examination of the fetal pelvis will demonstrate only one umbilical artery lateral to the bladder in its course toward the umbilical cord

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Cases and figures

  • Case 1: with esophageal atresia
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  • Case 2
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  • Case 3
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  • Case 4: with duodenal atresia and polyhydramnios
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  • Case 5
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