The umbilical cord connects a pregnant person and their developing baby throughout gestation. This structure facilitates the exchange of substances necessary for the baby’s growth. It is the primary conduit through which the fetus receives nourishment and oxygen, while also expelling waste products.
The Typical Umbilical Cord Structure
A typical umbilical cord, often called a three-vessel cord, contains two umbilical arteries and a single umbilical vein. These vessels are encased within Wharton’s jelly, a protective, gelatinous substance. Wharton’s jelly cushions and supports the blood vessels, safeguarding them from compression or kinking.
The umbilical cord also exhibits a spiral or coiled appearance along its length. This coiling, which forms by the ninth gestational week, protects the cord from external pressures and maintains its structural integrity. At term, the average umbilical cord measures approximately 50 to 60 centimeters in length and about 2 centimeters in diameter.
The Role of Umbilical Blood Vessels
The umbilical vein and arteries perform distinct functions in supporting fetal development. The single umbilical vein transports oxygenated, nutrient-rich blood from the placenta to the fetus. This blood supports the baby’s growth and organ development.
Conversely, the two umbilical arteries carry deoxygenated blood and metabolic waste products, such as carbon dioxide, from the fetus back to the placenta. There, this blood and waste are exchanged for oxygen and nutrients from the maternal circulation. This exchange system sustains fetal life and ensures healthy development.
Understanding Variations in Umbilical Artery Count
A common variation in umbilical cords is the presence of only one umbilical artery, known as Single Umbilical Artery (SUA). This condition, sometimes called a two-vessel cord, occurs in approximately 0.5% to 1.5% of singleton pregnancies and about 5% of twin pregnancies. The exact cause of SUA is not always clear, but it can arise if one artery does not develop fully or closes off early in pregnancy.
SUA is often detected during routine prenatal ultrasounds, typically in the second trimester. Further investigation, such as detailed ultrasounds or fetal echocardiograms, may be recommended to assess for associated conditions. In about 75% of cases, SUA is an isolated finding, meaning the baby is otherwise healthy and develops normally.
However, SUA can be associated with other fetal anomalies, including issues with the heart, kidneys, gastrointestinal system, or skeletal structure. Chromosomal abnormalities, such as Trisomy 13, 18, or 21, are also more frequently observed. If SUA is detected, medical follow-up monitors fetal growth and development, and investigates any associated conditions.