What is the role of the ductus venosus in fetal circulation?

The ductus venosus plays a critical role in fetal circulation by redirecting blood from the umbilical vein to the inferior vena cava. In the fetus, the primary source of oxygenated blood comes from the placenta through the umbilical vein. The ductus venosus allows a significant portion of this oxygen-rich blood to bypass the liver, which is not fully developed and functional during fetal life. Instead, this blood enters directly into the inferior vena cava and is subsequently directed into the right atrium of the heart.

By facilitating this shunt, the ductus venosus ensures that oxygenated blood is preferentially routed to vital structures such as the heart and brain, maximizing oxygen delivery to these critical areas. After birth, the ductus venosus closes and becomes a fibrous remnant known as the ligamentum venosum, as the newborn begins to rely on its lungs for oxygenation.