Pre-implantation genetic diagnosis (PGD or PIGD) is the genetic profiling of embryos prior to implantation (as a form of embryo profiling).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. Embryos are generally obtained through blastomere or blastocyst biopsy. The latter technique has proved to be less deletereous for the embryo, therefore it is advisable to perform the biopsy around day 5 or 6 of development.
The PGD allows studying the DNA of eggs or embryos to select those that carry certain mutations for genetic diseases. It is useful when there are previous chromosomal or genetic disorders in the family and within the context of in vitro fertilization programs.