Single umbilical artery on ultrasound: confirmation, associations and follow-up

A single umbilical artery is a cord with one artery and one vein, confirmed on a cord cross-section or with color Doppler around the fetal bladder. SMFM cites an incidence of 0.25 to 1% in singletons and up to 4.6% in twins. The question that drives management is whether the finding is isolated.

How to confirm it

• Cord cross-section: two lumens instead of three.
• Color Doppler in the fetal pelvis: only one artery running alongside the bladder. SMFM notes this allows detection even at early gestational ages.
• Side: ISUOG describes absence of the left artery as more common, but at least one series showed a similar split between sides. The sources reviewed do not link the side to different management.

Isolated or associated

Per SMFM, an isolated marker is one with no structural anomaly, growth restriction or additional marker after a detailed scan. The finding is therefore an indication for careful anatomic assessment.

• Co-occurring anomalies most often involve the cardiovascular and renal systems.
• Heart: if the required views are adequate and normal, SMFM does not consider fetal echocardiography routinely warranted.
• With an associated structural anomaly, the frequency of aneuploidy ranges from 4 to 50%.
• Isolated: no apparent increase in aneuploidy risk. SMFM recommends no additional evaluation, even if screening was declined, and the Voskamp meta-analysis (928 pregnancies) also found no increase, noting heterogeneity.

Follow-up of a single umbilical artery: where sources differ

SMFM itself acknowledges conflicting evidence on growth restriction and bases its recommendation on stillbirth risk: in a population-based case-control study the odds ratio was 4.80. It advises notifying the pediatric provider at delivery; in one study, up to 7% had a structural anomaly on postnatal examination. In practice, follow-up depends on local protocol and the attending physician.

What the report should include

• Number of vessels and how it was confirmed (cord section, pelvic Doppler).
• Kidneys, bladder and heart: what was seen or what could not be characterized.
• Biometry, estimated weight and amniotic fluid.
• Whether it is isolated as of that scan, without claiming more than the scan allows.
• Sample impression: "Single umbilical artery, with no other anomaly identified on the current scan."
• Recommendations in their own section, citing the guideline followed.

Common mistakes

• Not checking the pelvis with color Doppler when the cord section is doubtful.
• Calling it isolated without having seen the heart and kidneys.
• Ordering aneuploidy workup for the isolated finding alone.
• Leaving the finding out of the impression, which is what reaches the pediatrician.
• Presenting it to the patient as an anomaly: ISUOG notes it is not one in itself.

See also our articles on fetal growth restriction and obstetric Doppler.

How Laudário helps

In the obstetric and second-trimester anomaly scan templates in Laudário, the Cord tab offers:

• Vessels as options: three vessels, single umbilical artery, more than three vessels or not assessed.
• Selecting single umbilical artery changes the description and records the finding in the impression.
• The twin template records the vessels of each fetus, and placental insertion has its own field.

Try it free for 15 days, no credit card required.

References

• SMFM, Prabhu M, et al. Consult Series #57: Evaluation and management of isolated soft ultrasound markers for aneuploidy in the second trimester. Am J Obstet Gynecol. 2021;225(4):B2.
• ISUOG Practice Guidelines (updated): performance of the routine mid-trimester fetal ultrasound scan. Ultrasound Obstet Gynecol. 2022;59:840-856.
• Voskamp BJ, et al. Relationship of isolated single umbilical artery to fetal growth, aneuploidy and perinatal mortality: systematic review and meta-analysis. Ultrasound Obstet Gynecol. 2013;42(6):622-628.