Pre-implantation genetic diagnosis (PGD or PIGD) refers to
genetic profiling of
embryos prior to
implantation (as a form of
embryo profiling), and sometimes even of
oocytes prior to
fertilization. PGD is considered in a similar fashion 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
preimplantation 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. The PGD allows studying the DNA of eggs or embryos to select those that carry certain damaging characteristics. It is useful when there are previous chromosomal or genetic disorders in the family and within the context of in vitro fertilization programs.