During pregnancy, the umbilical cord links the developing fetus to the uterus. One vein and two arteries transport blood, nutrients and waste products. Following birth, the cord is usually tied or clamped. It is cut and the cord and placenta are then often disposed of. But cord blood is rich in stem cells that can form new blood cells. These blood-forming stem cells can help treat conditions such as cancers, immune deficiencies and genetic disorders.