Cord blood, or umbilical cord blood, is blood that remains in the umbilical cord and placenta at the time of birth. This blood has typically been discarded following delivery. But once scientists discovered it was a rich source of stem cells, umbilical cord blood became a viable substitute to bone marrow in thousands of successful transplants.

What are blood-forming stem cells? These are primitive (early) cells found primarily in the bone marrow that are capable of developing into the three types of mature blood cells present in our blood - red blood cells, white blood cells, and platelets. Cord-blood stem cells may also have the potential to give rise to other cell types in the body.

Some serious illnesses (such as certain childhood cancers, blood diseases, and immune system disorders) require radiation and chemotherapy treatments to kill diseased cells in the body. Unfortunately, these treatments also kill many "good" cells along with the bad, including healthy stem cells that live in the bone marrow.

Depending on the type of disease and treatment needed, some children need a bone marrow transplant (from a donor whose marrow cells closely match their own). Blood-forming stem cells from the donor are transplanted into the child who is ill, and those cells go on to manufacture new, healthy blood cells and enhance the child's blood-producing and immune system capability