The umbilical vein plays a vital role in the development of a fetus, serving as a lifeline between the placenta and the growing baby. During gestation, this single vessel is responsible for transporting oxygen-rich and nutrient-filled blood directly from the mother’s placenta to the fetal circulation. Unlike adult veins, which typically carry deoxygenated blood, the umbilical vein highlights its specialized role in fetal life.
The Initial Transition
Immediately following birth, rapid closure of the umbilical vein occurs due to significant physiological changes within the newborn’s circulatory system. As the baby takes its first breaths, the lungs expand, and pulmonary blood flow increases, initiating the shift from placental to pulmonary respiration. The cessation of blood flow from the placenta, due to placental separation, uterine contractions, and cord clamping, triggers the initial stages of the umbilical vein’s transformation.
This abrupt change in blood flow and pressure causes the muscular walls of the umbilical vein to constrict, leading to a reduction in its lumen. The umbilical arteries typically close moments before the vein, allowing for a natural “autotransfusion” of approximately 80-100 milliliters of blood from the placenta to the newborn. This process, taking several minutes, helps ensure the infant receives an optimal blood volume before the umbilical vein fully closes.
From Vein to Ligament
The umbilical vein undergoes an anatomical transformation, converting from a functional blood vessel into a fibrous cord. This process, known as obliteration, typically begins within a week after birth. It involves a combination of thrombosis, where blood clots form within the vessel, and fibrosis, the formation of fibrous connective tissue.
The lumen of the umbilical vein gradually fills with this fibrous tissue, sealing it off. This remodeling ensures that the vessel, no longer needed for blood transport, is converted into a solid, cord-like remnant. The final product of this transformation is the ligamentum teres hepatis, also commonly referred to as the round ligament of the liver.
This ligament extends from the umbilicus, ascending within the free margin of the falciform ligament, to the liver’s porta hepatis. While it loses its blood-carrying function, the ligamentum teres hepatis serves as an anatomical landmark in the adult body. Its transformation repurposes a temporary fetal structure into a permanent, non-circulatory component of the adult anatomy.
Clinical Perspectives
The timing of umbilical cord clamping after birth influences the final stages of the umbilical vein’s transition. Delayed cord clamping, typically performed 30 seconds to 5 minutes after birth, allows for continued blood transfer from the placenta to the newborn. This practice can increase the infant’s blood volume and iron stores, offering benefits such as reduced risk of iron deficiency anemia in infancy.
While the umbilical vein usually obliterates completely, rare instances of incomplete closure or anatomical variations occur. Conditions such as persistent right umbilical vein or umbilical vein varix are uncommon but can be identified during prenatal ultrasound. Many of these anomalies are benign, but some may warrant further evaluation to rule out associated developmental concerns.
In clinical settings, the obliterated umbilical vein, now the ligamentum teres, can sometimes be observed in adults, particularly in cases of severe liver disease like cirrhosis. While the umbilical vein itself does not “reopen,” the small veins adjacent to the ligamentum teres can become enlarged due to increased pressure, which differs from recanalization of the main umbilical vein.