What is preimplantation genetic testing or PGT?
Preimplantation genetic testing, PGT is essentially an alternative to prenatal diagnosis, in which genetic testing is performed on embryos produced by in vitro fertilization (IVF) before a pregnancy is established. There are three types of PGT, preimplantation genetic testing for aneuploidy (PGT-A), preimplantation genetic testing for monogenic disorders (PGT-M) and preimplantation testing for structural rearrangements (PGT-SR). Patients should consider PGT if any of the following conditions are present:
- recurrent pregnancy loss
- maternal age over 38
- prior unexplained IVF failures
- heritable medical condition in the patient or another child (such as cystic fibrosis)
- conception of a chromosomally abnormal child or fetus
- two or more children of the same gender (sex selection for family balancing)
Preimplantation genetic testing for aneuploidy, PGT-A
Aneuploidy is the presence of an abnormal number of chromosomes in a cell, with normal human cells having 46 chromosomes. Preimplantation genetic testing for aneuploidy (PGT-A) identifies embryos with the correct number of chromosomes. Utilizing PGT-A, we can separate chromosomally normal embryos from abnormal embryos, prior to implantation, so your care team can select the embryo with the best chance of IVF success. PGT-A can also be used to identify the gender of the embryo, prior to implantation.
Preimplantation genetic testing for monogenic/single gene defects, PGT-M
As a part of initial genetic screening, patients are tested for some known genetic disorders. If a patient or her partner is determined in this initial screening to have, or be a carrier, for a known genetic disease, Preimplantation genetic testing for monogenic/single gene defects (PGT-M) is recommended. PGT-M can be used to detect of single gene disorders present in embryos grown in vitro. This allows for an unaffected embryo (if available) to be selected for transfer.
The number of single gene disorders (diseases caused by inherited genetic defects) that can now be diagnosed with PGT-M continues to grow. Diseases such as cystic fibrosis, fragile X syndrome, myotonic dystrophy, thalassemia, and Tay Sachs disease can be diagnosed with PGT-M.
Preimplantation genetic testing for structural rearrangements, PGT-SR
Preimplantation genetic testing for structural rearrangements (PGT-SR) is appropriate for people who have a chromosome rearrangement, and thus are at risk of creating embryos with an incorrect chromosome number or structure. PGT-SR is recommended if you had a child or pregnancy with a chromosome rearrangement or if you or your partner are a known carrier of a translocation.
Like other types of PGT, PGT-SR involves testing embryos created through in vitro fertilization, IVF and then transferring only normal embryos.