Umbilical cord blood is a little-discussed byproduct of childbirth, something traditionally discarded after the baby arrives. But over the past two decades, a growing number of parents have turned to it as a potential lifesaver in case their children should develop any of a number of disorders. In the process, many of them have used a blood cord registry, whether public or private, for support.

Strictly speaking, cord blood is blood that stays in the umbilical cord after it is cut. In a broader sense, cord blood also refers to blood from the placenta. Both types are rich in hematopoietic stem cells, which is what makes cord blood valuable to parents and the medical community. Hematopoietic stem cells are used, often in place of bone marrow transplants, to treat certain some 70 medical conditions, and researchers are studying whether cord blood might help with other diseases.

There are two types of blood cord registry services that offer their support to parents looking to store cord blood: A public registry, where donors leave cord blood for the use of anyone who might need it, and a private registry, where parents pay to store cord blood for their child’s use, or for the potential use of another close relative.

Public banks can be few and far between, and once you’ve given them your child’s blood, there’s no promise you’ll get it back should your child need it. The use of a private bank, on the other hand, could cost a few thousand dollars, and the for-profit model of private banks has drawn harsh criticism in the medical community, much of which considers the practice of families storing cord blood for their exclusive use unethical and unnecessary.

All cord blood banks are regulated by the United States Food and Drug Administration. Private registries can also apply for accreditation by the American Association of Blood Banks or the Foundation for the Accreditation of Cellular Therapy.