Preimplantation Genetic Testing

Preimplantation genetic testing (PGT) is a procedure used with in vitro fertilization (IVF) to screen embryos for genetic conditions before they are transferred. The procedure involves removing 5-10 cells from the outer layer of an embryo, the trophectoderm layer which forms the placenta, and testing them for genetic disorders or chromosomal abnormalities. Embryos with normal test results are then transferred in order to increase the chance of a healthy pregnancy.  There are several types of PGT, including PGT-A (testing for chromosomal abnormalities), PGT-M (testing for specific genetic disorders), and PGT-SR (testing for structural rearrangements of chromosomes or translocations).

PGT-A can identify embryos that have an abnormal number of chromosomes, which can lead to conditions such as Down syndrome and Turner syndrome. Abnormal embryos are also responsible for causing miscarriages. PGT-A may benefit people over the age of 35 or with recurrent miscarriages or prior failed IVF cycles or embryo transfers. Pregnancy rates per embryo transferred are increased when a normal embryo is transferred and miscarriage rates are decreased. When PGT-A is used, embryos are transferred one at a time, reducing the risk of twins.

PGT-M, also known as preimplantation genetic testing for monogenic/single gene disorders, is a type of PGT used to screen embryos for a specific genetic disorder. Common uses are for screening embryos for Cystic Fibrosis, Sickle Cell Anemia, Tay-Sachs, Fragile X, or BRCA mutations. Embryos without these gene defects are selectively transferred to minimize the chance of having an affected child.