Blood flowing through umbilical vein of mammalian
embryo is
(1) 100% foetal (deoxygenated)
(2) 50% maternal (oxygenated) + 50% foetal
(deoxygenated)
(3) 50% maternal (deoxygenated) + 50% foetal
(oxygenated)
(4) 100% foetal (oxygenated)

Blood flowing in mammalian umblical cord is 100% foetal (deoxygenated). Umblical cord is an exception where arteries carry deoxygenated blood and veins carry the oxygenated blood (other exception is pulmonary vein and pulmonary artery). Hence, umblical vein carries nutrient rich, oxygenated blood towards the heart of the fetus whereas umblical artery carries deoxygenated blood away from the heart.