If you're pregnant, you've no doubt begun to hear a lot about cord blood. Here are the basics. First, the facts. After a baby is born and the umbilical cord is cut, some blood remains in the vessels of the baby's placenta and the cord attached to it. This is known as cord, or placental, blood. Cord blood has all the elements of normal blood, plus a rich supply of hematopoietic, or blood-forming, stem cells. These are similar to the cells found in bone marrow. For this reason, cord blood is increasingly replacing bone marrow in stem cell experimentation. In addition, cord blood transfers can be used to treat and improve some pediatric cancers and blood disorders. Today, cord blood can only be transplanted from a donor into a recipient who is a match. This is similar to how a bone marrow transplant works, although cord blood transplants use less stringent matching criteria. The cord blood from a baby will also have a high likelihood of matching with the baby's parents and any of the baby's siblings, so the benefits of familial cord blood extend beyond the donor. As of today, only a few illnesses can be treated with cord blood, so it is statistically unlikely that any individual will need the use of his or her cord blood. But because stem cell research is always evolving, many people believe that cord blood will have even more uses in the future.