Likelihood of use
The likelihood of using cord blood in private banks has rested mostly on the odds that the donor child or a family member will require a stem cell transplant. In the United States, the lifetime probability (up to age 70) that an individual will undergo an autologous transplant of their own stem cells is 1 in 435, the lifetime probability to undergo an allogeneic transplant of stem cells from a donor (such as a sibling) is 1 in 400, and the overall odds of undergoing any stem cell transplant is 1 in 217.[19] These figures are based on actual transplant rates in 2001-2003.

Cord blood transplants require less stringent matching between the tissue types of the donor and patient, known as their HLA types Human leukocyte antigen. Bone marrow transplants require a complete match on six key antigens, which are measures of graft-versus-host reaction, known as a 6/6 match. Cord blood transplants achieve the same medical success with only a 4/6 match. HLA type is inherited from both parents, so siblings are particularly likely to be a match, and people from the same ethnic heritage are more likely to match. Minority ethnic groups have difficulty finding a perfectly matched transplant donor; for them, the ability to transplant partially-mismatched cord blood opens access to transplant therapy. The Stem Cell Act of 2005 mandated HRSA to fund public cord blood banks to recruit more cord blood donations from ethnic minorities [3].

Studies have found that allogeneic transplants have better outcome when the donor and patient are related (because, in addition to those six key antigens, so many other antigens match)[20]. The odds that two siblings will have the 6/6 match required for a bone marrow transplant are 25%. The odds that two siblings will have the 4/6 match required for a cord blood transplant are 39%.