Why I chose to do PGT testing on my embryos: the summary

If you are embarking on an IVF cycle, its likely that you’ve been asked about doing “PGT Testing”. I want to share my experience with PGT, why we chose to do PGT testing on our embryos and the factors that played into that decision. But before that discussion, its important that you have an understanding of the terms and procedures.

This is not medical advice, I’m simply sharing knowledge that I’ve picked up from being a fertility patient for several years. Please consult your medical professionals for medical advice that is specific to your situation.

Firstly, what the heck is PGT? and is it different from PGS? (And why does the list of TTC acronyms keep growing?)

Some definitions before we jump in:

PGS stands for Preimplantation Genetic Screening. In most embryo labs, PGS has been replaced by PGT.

PGT stands for Preimplantation Genetic Testing. There are currently three types of test performed with PGT. (More on this below!)

Euploid is an embryo with the correct amount of chromosomes: 46.

Aneuploid is an embryo with an abnormal amount of chromosomes (these results will hugely vary).

Mosaic is an embryo with an undetermined profile of chromosomes - these are classified as High Level Mosaics or Low Level Mosaics and have a lower chance of successful implantation.

The process of Preimplantation Genetic Testing.

When an embryo created through in vitro fertilization (IVF) reaches the blastocyst stage, typically at 5 or 6 days after fertilization, they are developed enough to have PGT testing performed.

For PGT, an embryologist will perform a biopsy on an embryo and remove 5-10 cells. These cells are from the trophectoderm, the outer layer of cells that will become the placenta (not the baby!). The cells that are removed are then tested. After biopsy, the embryos themselves are carefully vitrified (frozen) until you make a decision on if or when to use them.

Check out this PGT biopsy video by instagram account @alease_the_embryologist.

What are the types of testing?

When most people refer to PGT, they are referring to PGT-A. However, there are now four different tests that can be performed on embryos, and I suspect this will grow in the next few years of scientific development!

PGT-A, which stands for Preimplantation Genetic Testing for Aneuploidy. This test counts the number of chromosomes (always looking for 46!) in each cell. If an embryo has an abnormal number of chromosomes (and rated as an aneuploid), it’s likely that this embryo will fail to implant in the womb or will miscarry in utero.

PGT-M, which stands for Preimplantation Genetic Testing for Monogenic Disorders. This test identifies genetic disorders that can be passed from one or both parent, such as cystic fibrosis or sickle cell anemia.

PGT-SR, which stands for Preimplantation Genetic Testing for Structural Rearrangements. This test identifies euploid embryos when one or more parents have Chromosomal translocation (often referred to as “balanced translocation”).

PGT-P, which stands for Preimplantation Genetic Testing for Polygenic Disorders. This test identifies genetic profiles which could lead to certain types of illness. This is not as clear cut as a monogenic disorder (PGT-M) where an embryo would be guaranteed to have the genetic disorder, but rather the embryo would be a carrier of certain cells that could put them at risk for disease later in life. A good example of this is the BRCA1, the gene that indicates high risk of breast cancer. This test is currently only offered at a handful of clinics worldwide.

Another great informational video from Alease the Embryologist explaining the different versions of PGT tests.

Who is recommended to do the testing?

It's important to note that PGT testing is a personal decision that should be made after careful consideration and consultation with a medical professional. The type of PGT test that is recommended will depend on individual circumstances and personal preferences.

The decision to use PGT testing should be one made with the guidance of your medical team. Primarily, most people choosing PGT for their embryos are testing for aneuploidy. But there are situations for all types of PGT testing.

PGT-A: this testing is not usually recommended for female patients younger than 35. Exceptions to this would be women who’ve suffered recurrent pregnancy loss (RPL).

PGT-M: this test is recommended for parents who are known carriers of genetic diseases. Sometimes people know they have a genetic disease in the family, other times things are discovered during prenatal genetic screening tests. This test will also be recommended to parents who’ve had miscarriages due to genetic disorders.

PGT-SR: As mentioned above, this test is typically for people who have a known case of chromosomal translocation. If you have chromosomal translocation (unbalanced or balanced), your rates of aneuploid embryos and miscarriages will usually be higher. This test will also be recommended to parents who’ve had miscarriages due to genetic disorders.

PGT-P: This is a test done for families with history of polygenic disease. While this testing isn’t available at every lab, it would be considered for couples with family history of breast cancer, type 2 diabetes, schizophrenia and more.

What is the hoped for outcome, what are the risks?

By choosing PGT testing, it’s hoped that euploid embryo transfers will lead to higher rates of implantation and even live births. Statistically, avoiding aneuploid embryo transfers will lower the risk of miscarriage.

I hope you found this helpful in understanding the different types of PGT testing. Look for part two- my personal experience with PGT coming soon!