Prenatal diagnosis and preimplantation genetic diagnosis: novel technologies and state of the art of PGD in different regions of the world.

Prenatal diagnosis (PND) aims to provide accurate, rapid results as early in pregnancy as possible. Conventional PND involves sampling cells of foetal origin by chorionic villus sampling at 11-14th weeks of pregnancy or amniocentesis after 15th week. These are invasive procedures and have a small but significant rate of 0.5% to 1% for loss of pregnancy. An alternative to existing methods for conventional PND for couples at risk of transmitting a genetic disease to their child is preimplantation genetic diagnosis (PGD). PGD is a newly emerging form of a very early prenatal diagnosis. The technique combines assisted reproductive technology with molecular genetics and cytogenetics to allow the identification of abnormality in embryos prior to implantation. The diagnosis of genetic disease in human preimplantation embryos was pioneered in the late 1980s for testing of aneuploidy, single gene and X-linked disease, such as cystic fibrosis, haemophilia and chromosomal abnormalities. The PGD-related legal and ethical issues have been debated at many levels both nationally and internationally. The attitude towards PGD varies substantially not only in different parts of the world but also within the Europe, owing to scientific, cultural and religious differences. PGD has become widely practised throughout the world for various indications and can substantially decrease the eventual risks of passing a genetic undesired condition of the offspring. Nevertheless, its extension to some new and non-medical indications has raised ethical concerns, in particular its potential eugenic dimension.