The umbilical cord is a narrow tube-like structure that connects the developing baby to the placenta. Long considered a biological waste, the blood in the umbilical cord is now recognized as a valuable source of stem cells. Stem cells from umbilical cord blood help improve treatments for persons with such serious illnesses as leukemia, anemia and medullary aplasia in which the bone marrow does not produce enough blood cells. In the embryo, a vessel that connects the left umbilical vein with the inferior vena cava, enabling blood to bypass the developing venous system in the liver. After birth, the ductus venosus is obliterated and forms the ligamentum venosum. The measurement of hypxanthine, xanthine, inosine and uridine in umbilical cord blood and fetal scalp blood samples as a measure of fetal hypoxia.