Preimplantation genetic diagnosis, an alternative to conventional prenatal diagnosis of the hemoglobinopathies.

Prenatal diagnosis (PND) and preimplantation genetic diagnosis (PGD) both represent highly important reproductive choices for couples with a high risk of transmitting a severe disease, such as a severe hemoglobinopathy. Conventional PND for hemoglobinopathies based on molecular analysis of trophoblast or amniocyte DNA has been applied for around 30 years, but the major disadvantages with this approach include 'invasive' fetal sampling, and the potential involvement of pregnancy termination when affected. In comparison, the major advantage of PGD over conventional PND is that it supports the initiation of unaffected pregnancies, avoiding the need to terminate affected pregnancies. However, it is a multistep technically demanding procedure requiring the close collaboration of experts from several fields. PGD is also limited by the need to involve assisted reproduction, even in couples without fertility problems. Furthermore, even for fertile couples, pregnancy rates rarely surpass 30-35%. Both PND and PGD have advantages and drawbacks. Before embarking on either procedure, couples should be carefully counseled by experts so that they can select the option most appropriate for them. Finally, whatever their choice, it is paramount that both prenatal and PGD be applied with the highest standards of clinical, laboratory, and ethical practice.