[Preimplantation genetic diagnosis: technical and ethical considerations].

Following the advances in the techniques of medically assisted reproduction (ART), 1990 has seen the first born child after the development of pre-implantation genetic diagnosis. In this analysis embryos are tested for the presence of genetic anomalies at three to five days after fertilization and only unaffected embryos are transferred to the maternal uterus. The technique offers good prospects to couples at risk for conventional prenatal diagnosis. It is particularly useful where ART techniques are necessary, in which early embryo selection avoids later termination of pregnancy. In Portugal the application of laws concerning regulation of medically assisted reproduction in 2008 has clarified and formalised the medical and laboratory procedures and in some cases fundamentally changed them, particularly in the requirement to cryopreserve all high quality non-transferred embryos and in specifying conditions in which embryo experimentation may be permitted.