PGT: When is Preimplantation Genetic Testing an Option?
By Michael Zinger, MD, FACOG
Preimplanatation Genetic Testing (PGT) is a procedure that screens embryos for genetic abnormalities before they are transferred into the uterus. PGT can be used for couples of normal fertility that have been identified as high-risk for passing on a genetic disease as well as for couples experiencing fertility problems who wish to avoid a maternal-age related increase risk of birth defects.
PGT is subdivided into three categories:
- PGT-M (previously referred to as PGD) is testing for a monogenic (single-gene) mutation that is known to be carried by one or both parents.
PGT-M can be performed to help couples aware of genetic disorders through family history or based on carrier testing. In genetic disorders where the genetic mutation is known, such as Cystic Fibrosis or Tay-Sachs, the actual genes of the embryo are examined for presence of the condition and only the normal embryos are transferred back to the mother.
- PGT-SR is testing for a structural rearrangement of chromosomes that is known to be carried by a parent.
In the case of recurrent miscarriages, if karyotype of the parents reveals that one of them has a balanced translocation, then PGT-SR can be used. This will identify which embryo is destined to fail (or have defects) due to inheriting an unbalanced portion of the translocation.
- PGT-A (previously referred to as PGS) is testing for aneuploidy (an abnormal number of chromosomes) in the embryo.
Unlike the first two categories, embryos are typically predisposed to aneuploidy based on maternal age rather than any known genetic problem with the parents. Aneuploidy is the most common cause of failed IVF cycles and of early pregnancy loss. It can also lead to birth defects such as Down Syndrome. PT-A avoids these problems by determining the number of each chromosome and, thus, which embryos are the most likely to result in a healthy pregnancy. Further, by selecting out euploid embryos, PGT-A allows us to maintain excellent success rates with single-embryo transfers at any age, thus minimizing the risk of multiple pregnancy. Another benefit for some families is identification of the sex chromosomes, which allows parents to specify a gender preference, balancing families whose previous children all one gender.
Testing: Accuracy and Process
The accuracy of PGT depends upon the disease being tested for, but overall it is able to diagnose genetic defects with a very high accuracy. The advantage of PGT is that it reveals these genetic defects before pregnancy, as opposed to amniocentesis or CVS being performed during pregnancy.
The PGT process begins with the same steps taken during preparation for a normal IVF cycle. Once the embryos have developed, one or more cells are taken from each embryo for analysis. At RMA Long Island IVF our expert embryologists are trained in the most recent biopsy techniques to help insure the highest quality of results.
If you would like to discuss the PGT process further, or have any questions, please don’t hesitate to contact me at (516) 358-6363 or firstname.lastname@example.org