Umbilical cord blood is blood that remains in the placenta and the attached umbilical cord after childbirth. Since a newborn no longer requires cord blood after birth, it is as a rule discarded along with the placenta and umbilical cord. Cord blood contains mature blood cells along with a small number of stem cells that take part in the renewal of a body by dividing and maturing into various types of mature cells which replace old and damaged cells of tissues and organs.

After childbirth, cord blood is taken and stored as a source of haematopoietic and other stem cells to be used for treating diseases by cell transplant. Presently, this method is used to cure certain blood cancers and inherited disorders of metabolism and the immune system. The treatment of other diseases (such as the Alzheimer's and Parkinson's disease, cardiac and liver diseases, diabetes, muscular dystrophy, multiple sclerosis, spinal cord injury, etc.) is still under investigation.

When treating diseases with stem cell transplant, umbilical cord blood has certain advantages over bone marrow or haematopoietic stem cells harvested from peripheral blood due to its special biological and other characteristics, such as easy and improved access, low risk for the transmission of viral infections and low risk for the emergence of graft-versus-host disease after the transplant. The major disadvantages of cord blood are a small number of haematopoietic stem cells, which presently suffice merely for the treatment of children weighing less than 25kg, and a long period of time required for such graft to take hold.