After a baby is born and the umbilical cord is cut, some blood remains in the blood vessels of the placenta and the portion of the umbilical cord that remains attached to it. After birth, the baby no longer needs this extra blood. This blood is called placental blood or umbilical cord blood: "cord blood" for short.

Cord blood contains all the normal elements of blood - red blood cells, white blood cells, platelets and plasma. But it is also rich in hematopoietic (blood-forming) stem cells, similar to those found in bone marrow. This is why cord blood can be used for transplantation as an alternative to bone marrow.

Cord blood is being used increasingly as a source of stem cells, as an alternative to bone marrow. Most cord blood transplants have been performed in patients with blood and immune system diseases. Cord Blood transplants have also been performed for patients with genetic or metabolic diseases. More than 80 different diseases have been treated to date with unrelated cord blood transplants