Preimplantation Genetic Diagnosis

Preimplantation Genetic Diagnosis

In medicine and (clinical) genetics pre-implantation genetic diagnosis (PGD or PIGD) (also known as embryo screening) refers to procedures that are performed on embryos prior to implantation, sometimes even on oocytes prior to fertilization. PGD is considered another way to prenatal diagnosis. When used to screen for a specific genetic disease, its main advantage is that it avoids selective pregnancy termination as the method makes it highly likely that the baby will be free of the disease under consideration. PGD thus is an adjunct to assisted reproductive technology, and requires in vitro fertilization (IVF) to obtain oocytes or embryos for evaluation.

The term pre-implantation genetic screening (PGS) is used to denote procedures that do not look for a specific disease but use PGD techniques to identify embryos at risk. PGD is a poorly chosen phrase because, in medicine, to "diagnose" means to identify an illness or determine its cause. An oocyte or early-stage embryo has no symptoms of disease. They are not ill. Rather, they may have a genetic condition that could lead to disease. To "screen" means to test for anatomical, physiological, or genetic conditions in the absence of symptoms of disease. So both PGD and PGS should be referred to as types of embryo screening.

The procedures may also be called preimplantation genetic profiling to adapt to the fact that they are sometimes used on oocytes or embryos prior to implantation for other reasons than diagnosis or screening.

Procedures performed on sex cells before fertilization may instead be referred to as methods of oocyte selection or sperm selection, although the methods and aims partly overlap with PGD.