Preimplantation genetic diagnosis (PGD) is a reproductive technology used along with an IVF cycle to increase the potential for a successful pregnancy and delivery. PGD is a genetic test on cells removed from embryos, to help select the best embryo(s) to achieve pregnancy or to avoid a genetic disease for which a couple is at risk.
PGD may be considered in all IVF cycles; however, those who might benefit most from this test are couples at increased risk for chromosome abnormalities or specific genetic disorders. This includes women who have had several miscarriages, or who have had a prior pregnancy with a chromosome abnormality. Women over 38 years of age and men with some types of sperm abnormalities may produce embryos with higher rates of chromosome abnormalities. This test is also known as PGT-A (aneuploidy). In addition, if a person carries a structural rearrangement of the chromosomes, PGD can identify which embryos have a normal amount of chromosomal material. This technology is also known as PGT-SR (structural rearrangement). When there is a 25% or 50% chance to have a child affected with a specific genetic disease, PGD can be designed to identify which embryos are affected, unaffected, or a carrier (if applicable) for that disease. Then, only embryos without the disease are transferred to the uterus to attempt pregnancy. This is also known as PGT-M (monogenic disorders).
After embryos are created in the laboratory, they are grown for five to six days. On day five or on day six, the biopsy for PGD is done on all appropriately developing embryos. Biopsy involves removing a few cells from the trophectoderm, or the layer of cells that is ‘hatching out’ of the embryo at this stage of development. The embryos are stored while genetic material inside the removed cells is tested for abnormalities. One of Genetic & IVF’s genetic counselors discusses PGD test results with the woman/couple, and a frozen embryo transfer (FET) cycle is planned for use of the embryo(s). Decisions regarding selection of embryos to transfer into the uterus are made with the advice of both the medical and genetics team.
The Steps that Lead Up To fertilisation are the same as any ivf procedure. Then as usual the egg is allowed to fertilize with the sperm.