Difference Between Genetic Carrier Screening and PGT testing
Initially getting started with fertility treatment can be overwhelming, especially since there are a lot of new terms that are being used. I am here to clarify one of the commonly asked questions: Is it necessary to have the genetic carrier screening drawn if I’m planning on doing PGT testing? Although technically the answer is no, you do not have to do the genetic carrier screening, this testing is highly recommended in addition to PGT testing, as they are completely different tests.
Let’s start by discussing what genetic carrier screening entails. A genetic carrier screening is a test that is done during the diagnostic phase of treatment (initial testing) to check if you are a carrier for specific genes/disorders. IHR uses Invitae’s Comprehensive Carrier Screen which currently is able to test for 289 genes. If your genetic carrier screen results indicate that you are a carrier for a specific gene, that means that your partner also needs to be tested to ensure that they are NOT carriers for that specific gene. If your partner’s genetic carrier screen results indicate that they are a carrier for the same gene that you are a carrier for, then this means that a more advanced version of the PGT testing will need to be completed on the embryos (PGT-M) to determine which embryos are not affected by the specific gene that you and your partner are carriers for.
Now let’s discuss PGT testing. PGT testing stands for preimplantation genetic testing, and it is testing that is done on the embryo itself. After an IVF cycle, the eggs will be inseminated with the sperm and the embryos will grow for 5-7 days until they reach the blastocyst stage of development. At that time, the embryos are biopsied (a small amount of cells are taken from the embryo) and the biopsy is sent to a different lab for PGT testing, while the embryo itself is frozen at IHR’s lab. There are a few different types of PGT testing, including PGT-A, PGT-M, and PGT-SR.
- PGT-A testing stands for preimplantation genetic testing for aneuploidies, which means that the test is looking at the chromosomal alignment of each embryo to determine if the embryo is normal (euploid), or abnormal (aneuploid).
- PGT-M testing stands for preimplantation genetic testing for monogenic/single gene defects. Most commonly, the need for PGT-M testing is determined through the genetic carrier screening as indicated above, but we also can determine the need for PGT-M testing through some individual’s familial background.
- PGT-SR testing stands for preimplantation genetic testing for chromosomal structural rearrangements.
By having the PGT results of the embryos, the physician is able to choose the best embryo for transfer, which in turn increases the success rates for a healthy pregnancy and birth.
All in all, both the genetic carrier screening and the PGT testing are tools that have been created to help provide more insight as to why couples may be having a difficult time getting pregnant and/or staying pregnant. The more information that we are able to gather with these tests, the better chance we have to help you reach your dreams of growing your family.