Normal Umbilical Cord Anatomy
The normal umbilical cord contains one vein and two arteries. 1
Anatomical Structure
The umbilical cord consists of 2 arteries and 1 vein, all embedded in a gelatinous tissue called Wharton's jelly and covered by an outer layer of amnion. 2, 3
The single umbilical vein carries oxygenated blood from the placenta to the fetus, while the two arteries carry deoxygenated blood and waste products from the fetus back to the placenta. 4
This vascular configuration is established by the 12th week of gestation and represents the final form of the umbilical cord. 2
Clinical Significance of Abnormal Vessel Number
Single Umbilical Artery (SUA)
An SUA results from either primary agenesis or secondary atrophy of one of the two arteries, occurring in 0.25% to 1% of singleton pregnancies and up to 4.6% of twin gestations. 1, 4
When an SUA is detected on ultrasound, a comprehensive assessment of cardiac anatomy should be performed, as co-occurring structural abnormalities most commonly involve the cardiovascular and renal systems. 1
For isolated SUA with no other structural abnormalities, no additional evaluation for aneuploidy is recommended, regardless of whether previous aneuploidy screening was performed or declined, as there appears to be no increased risk of aneuploidy in this setting. 1
Third-trimester ultrasound to evaluate growth and consideration of weekly antenatal fetal surveillance beginning at 36 0/7 weeks of gestation is recommended for fetuses with isolated SUA, given conflicting evidence but documented increased risks of stillbirth (OR 4.80; 95% CI 2.67-8.62). 1
Detection Method
- An SUA can be detected on cross-section of the umbilical cord during routine second-trimester ultrasound examination, and color flow Doppler can be used to examine the umbilical arteries in the pelvis even at early gestational ages. 1