Single umbilical artery

A 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 some unknown reason, absence of the left umbilical artery is much more common (~70%) .

The estimated prevalence is at ~0.4-1% of pregnancies 5-6,10. There can be an increased incidence in twin pregnancies and with 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 often approaches the size of the umbilical vein (which in a normal situation is usually larger than the artery). 

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


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

Recognised 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

Antenatal ultrasound

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

  • shows two vessels within the umbilical cord (one artery and one vein) instead of the three (best seen in cross section)
  • the single artery is often larger in calibre 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

When found in isolation, it is usually not of clinical significance but there is an increased incidence of intra-uretine growth restriction (IUGR) 6 ( ~15%). It is however a concern when concurrent anomalies are found due to association with other fetal anomalies in such circumstances. 

Ultrasound - obstetric
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Article information

rID: 10823
Section: Pathology
Synonyms or Alternate Spellings:
  • Single umbilical artery (SUA)
  • Solitary umbilical artery
  • Two vessel cord
  • Two vessel umbilical cord
  • Two vessel cord (TVC)
  • TVC
  • 2VC
  • 2 vessel cord

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