Preimplantation Genetic Testing for Aneuploidy (PGT-A) is an optional genetic test performed on embryos created through IVF.
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.
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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.
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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).
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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.
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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
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Egg Retrieval & Fertilization: Eggs are retrieved from the ovaries (or thawed) and fertilized with sperm to create embryos.
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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.
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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).
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Freezing: The biopsied embryos are immediately frozen and safely stored. Only the removed cells are sent to the genetic testing laboratory.
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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:
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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.
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Reduced Risk: It lowers the risk of early pregnancy loss per embryo transferred.
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Time Efficiency: It may reduce the number of embryo transfer procedures needed to achieve pregnancy and reach your family building goals.
Important Limitations
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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.
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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%.
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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.
