What is PGT?
Preimplantation genetic testing (PGT) is a screening test to determine if an embryo has certain genetic abnormalities before it is transferred into the uterus following IVF. Until recently, PGT was only completed following an embryo biopsy procedure. During this procedure, 5-10 cells are removed from an embryo and the embryo is frozen afterward. A new method known as non-invasive PGT is also now routinely used. Non-invasive PGT analyzes the culture fluid that an embryo develops within.
There are three types of PGT:
PGT-A (aneuploidy): this is the most common type of PGT that is performed. It determines what percentage of an embryo’s cells have the right number of chromosomes.
PGT-M (monogenic): this type of PGT is reserved for couples who both carry a gene for the same disease, which puts their offspring at risk of having that genetic disease or carrying the gene for that disease. An example of this is cystic fibrosis. PGT-M can determine which embryos are affected by, carriers of, or unaffected by the genetic disease.
PGT-SR (structural rearrangement): this type of PGT is reserved for parents or couples who have a known chromosomal rearrangement such an inversion or translocation that can be passed onto their offspring. PGT-SR can determine which embryos are affected by these rearrangements.
Types of PGT-A results
Genetic testing companies have certain thresholds that they use to categorize embryos:
Euploid: most (usually 80% or more) of the embryo’s cells have the right number of chromosomes. These embryos are recommended for transfer.
Aneuploid: few (usually 20% or less) of the embryo’s cells have the right number of chromosomes. These embryos are not recommended for transfer.
Mosaic: some (usually 20-80%) of the embryo’s cells have the right number of chromosomes. It’s recommended that you speak with a genetic counselor before transferring a mosaic embryo.
Why is PGT-A important?
For PGT-A results, the higher percentage of cells with the right number of chromosomes, the higher chance that the embryo will implant and result in a healthy live birth. In fact, the leading cause of miscarriage is chromosomal abnormalities in an embryo. PGT-A is especially recommended for women over 35 years of age, which is when egg quality typically begins to decline.
