A variety of genetic disorders are treatable by allogeneic bone marrow transplantation. Predictive genetic testing and HLA typing of cultured fetal cells enable one to know early in a pregnancy that a fetus is genetically normal and is HLA-identical to a sibling affected with a genetic disease. Umbilical cord blood can be collected at the delivery of an HLA-matched normal sibling and used for stem/progenitor cell transplantation for the affected child. Our experience with families of children with Fanconi anemia has shown that the deliberate conception of a fetus for the possibility of providing a transplant donor is often undertaken. This paper reviews the genetic diseases potentially treatable by cord blood transplantation and the methods and pitfalls of prenatal testing for these conditions. Our laboratory's extensive experience with prenatal diagnosis for Fanconi anemia is discussed and provides the framework for an examination of the ethical issues related to the conception of a fetus for the purpose of providing a transplant donor.