Progress in prenatal diagnosis:

Polymerase-chain-reaction (PCR) technology has been used for more than a decade to detect point mutations or deletions in chorionic-villus samples, enabling first–trimester, DNA-based testing for thalassemia. However, because pregnancy termination is unacceptable to some persons (even when the fetus is affected), methods were developed, beginning in the early 1990s, to perform diagnostic testing before implantation (Rund and Rachmilewitz, 2005). PCR is then used to detect thalassemia mutations within the cells that have been removed so that unaffected blastomeres may be selected for implantation. Preimplantation genetic diagnosis requires a high degree of technical expertise. Furthermore, the phenomenon of "allele dropout"; failure to amplify one of the two alleles in a heterozygous cell can result in diagnostic errors. Nonetheless, this technology has been successful, and improvements in outcome have led to its use in many countries  (van de velde et al., 2004). Recently, preimplantation genetic diagnosis has been extended to HLA typing on embryonic biopsies, which allows the selection of an embryo that is not affected by thalassemia and that may also serve as a stem-cell donor for a previously affected child within the same family (Rund and Rachmilewitz, 2005).

Although it is considered ethical not to implant an embryo that is affected with a serious genetic disorder, in certain countries it is forbidden to select an embryo on the basis of its designated role as a potential stem-cell donor. Future prenatal diagnosis may to be performed non –invasively, with the use of maternal blood samples to isolate either fetal cells or fetal DNA for analysis (Di Naro et al., 2002).