PGT stands for “preimplantation genetic testing.” This is a technology that allows us to genetically test embryos prior to transfer and implantation. When a sperm fertilizes an egg, the embryo then divides from one cell to two cells to four cells, etc. until it becomes hundreds of cells! At this stage, the embryo is called a blastocyst and can undergo genetic testing.
Note: Due to the techniques involved, this testing can only be used when a patient is undergoing in vitro fertilization (IVF). IVF allows eggs to be fertilized in a laboratory. The resulting embryos can be tested before being transferred to the uterus.
How are the eggs tested?
A specialist in the lab (called an embryologist) extracts a sample of cells from the outer ring of the blastocyst. These cells are then genetically analyzed to help us better understand the chromosomal make-up of the embryo. There are two types of PGT: “PGT-A” and “PGT-M.”
PGT-A refers to testing the cells for “Aneuploidy”, which means an incorrect number of chromosomes. Embryos with the best chance for pregnancy are those that have 23 chromosomes from the egg and 23 chromosomes from the sperm, as most healthy pregnancies result from an embryo that contains 46 chromosomes.
PGT-M refers to testing the cells for a “Monogenic” disorder. For some patients/couples, their offspring may be at risk for a particular disorder if they carry a genetic mutation. One example is sickle-cell disease. If both partners carry a bad sickle-cell gene, there is a one if four chance that their child would be affected by sickle cell disease. Performing PGT-M allows us to know which embryos do NOT carry two bad genes, so that a healthy embryo can be implanted into the patient. PGT-A and PGT-M are not necessary or appropriate for all couples but your physician can help guide you in the decision-making process.