What is the primary vessel responsible for carrying oxygenated blood from the placenta to the fetus?

The umbilical vein is the primary vessel responsible for transporting oxygenated blood from the placenta to the fetus. During fetal development, the placenta serves as the site for gas exchange, where the mother's oxygen-rich blood is delivered to the placenta. The umbilical vein carries this enriched blood directly to the fetus, supplying it with the necessary oxygen and nutrients needed for growth and development.

In contrast, the umbilical arteries, which are branches of the iliac arteries in the mother, carry deoxygenated blood from the fetus back to the placenta for oxygenation. The pulmonary vein is involved in carrying oxygenated blood from the lungs to the heart in postnatal circulation, while the inferior vena cava is responsible for returning deoxygenated blood from the lower part of the body back to the heart. Thus, the umbilical vein's role is unique and crucial during fetal life, making it the correct answer.