Preimplantation Genetic Testing (PGT)
Preimplantation Genetic Testing (PGT) is performed through biopsy of an embryo. Several cells from an embryo are removed through an opening in the shell around the embryo (zona). These cells then undergo genetic testing using advanced molecular genetic techniques such Next Generation Sequencing (NGS). There are three types of Preimplantation Genetic Testing (PGT) based on the goal of the testing.
- Preimplantation Genetic Testing for Aneuploidy (PGT-A, formerly called PGS): The majority of IVF failures and miscarriages are due chromosomal abnormalities in the embryos. We all have 23 pairs of chromosomes. Unfortunately, embryos frequently have an extra (47 chromosomes) or a missing chromosome (45 chromosomes) which lead to genetically abnormal fetuses (such as Down’s Syndrome, Turner’s Syndrome), early miscarriage, or failure to achieve pregnancy. Identification of the embryos with the correct chromosome count leads to higher implantation/pregnancy rates per embryo transfer and lower miscarriage rates. Aneuploidy is the technical term for abnormal chromosome count due to a missing or an extra chromosome.
- Preimplantation Genetic Testing for Monogenic/single gene diseases (PGT-M, formerly called PGD): Recessively inherited genetic illnesses happen when the same an abnormal gene both the mother and father to be transmitted to the baby. If the parents are healthy carriers for the same recessively inherited genetic disease such Cystic Fibrosis or Sickle Cell Disease, we can test the embryos’ genes in a similar manner to PGT-A for that specific disease. We recommend screening our patients to see if they are carriers of some common recessively inherited genetic diseases even if they have no known family history.
- Preimplantation Genetic Testing for chromosomal Structural Rearrangements (PGT-SR): Chromosomes can get broken and imperfectly repaired in the cell growth process and produce a kind of “translocation” of part of one chromosome onto part of a different chromosome. This uncommon event may be diagnosed in a couple with a history of recurrent pregnancy losses or in some men with extremely low sperm counts. A parent who is a carrier of a translocated chromosome can still have genetically normal children. Similar to PGT-A, we can detect the embryo(s) that have the structurally normal chromosomes for the embryo transfer, which increases the pregnancy rate and decreases the miscarriage risk significantly.