What is PGD?

Pre-implantation Genetic Diagnosis (PGD), first developed in the 1980's, is the application of genetic testing on a live embryo to determine the presence, absence or change in a specific gene or chromosome prior to the placement of the embryo in the womb.

The first step to PGD is the creation of embryos outside the body by in vitro fertilisation (IVF). These embryos are cultured until they are between 6-10 cells, in size, on Day 3 of culture, so that one or two cells can be removed (cell biopsy) for genetic analysis. The removal of these cells does not appear to be detrimental to the development of the embryo. The "sampled" embryo can then be grown a little longer in culture to let it recover from the procedures and to allow time for the genetic testing of its removed cells to take place.

One of two techniques is then applied to the biopsy cells - flourescent in situ hybridisation (FISH) for chromosome disorders or - polymerase chain reaction (PCR) for single gene defects. Embryos which do not carry the genetic disorder tested can then be transferred to the uterus in the hope that a normal pregnancy will develop. Further analysis later in the pregnancy can then be offered to the couple by sampling the placental material (chorionic villus sampling) of the developing conceptus to confirm the PGD analysis.