PGT-A at Twig: Understanding Chromosomes, Embryo Health, and Your Options

Preimplantation Genetic Testing for Aneuploidy (PGT-A) is an optional genetic test performed on embryos created through IVF. It helps us prioritize transferring the embryos most likely to result in an ongoing pregnancy.

It is important to discuss PGT-A with your physician and genetic counsellor to make an informed decision that is right for you.

What PGT-A Screens For

PGT-A screens for the correct number of chromosomes in an embryo. Chromosomes are the structures within cells that contain all of our genetic information.

• Euploid Embryo: An embryo with the normal number of chromosomes (23 pairs, or 46 total). Transferring a euploid embryo has the highest chance of an ongoing pregnancy and a baby without a chromosomal condition.
• Aneuploid Embryo: An embryo with an abnormal number of chromosomes (more or less than 23 pairs). Most aneuploid embryos will not implant. Those that do most often result in early pregnancy loss (miscarriage).
• Mosaic Embyro: The embryo contains a mixture of both normal and abnormal cells. They carry a higher risk of abnormal development or miscarriage compared to fully euploid embryos, and their transfer is dependent on the percentage of abnormal cells.
• No Result/Inconclusive: Inconclusive results are often due to poor DNA quality or an insufficient cell sample. These embryos may be re-biopsied or thawed and re-tested if frozen.

The risk of creating aneuploid embryos increases with the age of the egg.

The PGT-A Process

1. Egg Retrieval & Fertilization: Eggs are retrieved from the ovaries (or thawed) and fertilized with sperm to create embryos.
2. Blastocyst Culture: Embryos are cultured for 5 to 7 days until they reach the blastocyst stage (100–200 cells). “Cultured” refers to the process of growing fertilized eggs (embryos) in the laboratory for several days to support their development.
3. Biopsy: A procedure in which 5 to 10 cells are carefully removed from the outer layer (the trophectoderm) of the embryo. This layer of the embryo goes on to form the placenta (not the baby).
4. Freezing: The biopsied embryos are immediately frozen and safely stored. Only the removed cells are sent to the genetic testing laboratory.
5. Results: After approximately 2–3 weeks, your results are ready and reviewed with you by a Twig genetic counsellor.

Benefits of PGT-A

Preimplantation genetic testing benefits include:

• Increased Chance of Success: Selecting a euploid embryo to transfer can increase the chance of implantation and pregnancy per embryo transferred. This is particularly true when the age of the egg provider is over 35.
• Reduced Risk: It lowers the risk of early pregnancy loss per embryo transferred.
• Time Efficiency: It may reduce the number of embryo transfer procedures needed to achieve pregnancy and reach your family building goals.

Important Limitations

• Prioritization tool: PGT-A does not increase the likelihood that one full cycle of IVF will lead to a child; it is an embryo selection and prioritization tool.
• Not 100% Accurate: The test is highly accurate but not 100% perfect. The chance of a false positive or false negative result is thought to be less than 2%.
• Freezing Required: To perform PGT-A, all embryos must be frozen and then thawed for a subsequent transfer cycle.

Interested in PGT-A? Click here to book a complimentary family building consult. No referral required.