What is PGT-A? Embryologists explain what it tests and how they do it.
If you are exploring embryo donation, you may come across the term PGT-A and wonder what it means for the embryos involved. Genetic testing is a common part of the IVF process, and many donated embryos have already been tested before they are ever made available.
In this video, embryologist Gina McCain of Sanford Women's Health and Michael Baker, PhD, of Aspire Fertility explain what PGT-A tests for, how the biopsy is actually done in the lab, and the benefits and trade-offs worth understanding. Our goal is simply to help you feel informed, whether you are a donor or a recipient.
What PGT-A Is
PGT-A, or preimplantation genetic testing for aneuploidy, is the most common form of genetic testing in IVF laboratories.
In PGT-A, a few cells are taken from the trophectoderm of the embryo (the outer layer of cells that goes on to become the placenta) and sent to a genetic testing lab. There, the lab analyzes the total number of chromosomes present in the embryo. That chromosome count gives confidence about whether the embryo has the chromosomes needed for a viable pregnancy.
If you choose to have the information disclosed, PGT-A can also reveal the embryo's biological sex.
You may have heard PGT-A called PGS (preimplantation genetic screening) in the past. That is an older name for the same general type of testing.
PGT-A vs PGT-M: Two Different Questions
It helps to separate two kinds of genetic testing, because they answer different questions.
PGT-A looks at the number of chromosomes. It tells you whether an embryo is euploid (a normal chromosome count) or aneuploid (an abnormal count). An aneuploid result can mean an embryo has too many chromosomes, called a trisomy, or too few, called a monosomy.
PGT-M, or preimplantation genetic testing for monogenic disorders, looks at specific genes. This was previously known as PGD (preimplantation genetic diagnosis). PGT-M is used when a particular inherited condition is known to run in a family, so the lab looks at very specific genes and mutations. Families have pursued PGT-M for conditions such as Fragile X syndrome, Huntington's disease, cystic fibrosis, and BRCA mutations.
In short: PGT-A counts chromosomes, while PGT-M looks for a known single-gene condition.
How the Biopsy Is Done
To run PGT-A, the lab needs to biopsy somewhere between three and eight cells from the trophectoderm layer. If no cells can be removed from that layer yet, the embryo simply is not ready to be biopsied, so it is cultured for another day.
Here is what happens during the biopsy itself:
Only the trophectoderm is sampled, the outer layer that becomes the placenta. The inner cell mass, the part that develops into the fetus, is deliberately left untouched.
The embryo is held gently in place with a holding pipette on one side of the field so the cells do not float away.
A laser is directed at the junction between the trophectoderm cells, and a small section of that outer layer is carefully separated from the main part of the embryo.
The biopsied piece is sent to the genetic testing lab, and the embryo itself is frozen and kept at the clinic while results are pending.
It is a delicate, precise process. Handled carefully, the cells release cleanly from the embryo.
Weighing the Benefits and Trade-Offs
PGT-A is a powerful technology that helps many patients, but as the presenters in this video explain, it is worth understanding the trade-offs as well as the benefits.
There is a small risk that an embryo does not survive the biopsy process, though that risk is very low. Beyond survival, there is also some subtle stress placed on the embryo during biopsy. One way that shows up: the total number of live births from PGT-tested embryos can be somewhat lower than you might expect compared with transferring every untested embryo in the same group. That difference suggests the small amount of stress from biopsy may affect some embryos' implantation potential.
Whether that trade-off is worth it depends a lot on the situation. The video offers a useful way to think about it. When a high share of embryos is expected to be aneuploid, say around half or more, testing can be very valuable for identifying the embryos most likely to succeed. But when a large majority of embryos is expected to be euploid, say around 75 percent, some patients and their care teams may prefer to maximize the total number of live births per retrieval by transferring untested embryos one after another instead.
There is no single right answer to whether a family should test the embryos, or even what the outcomes mean. A patient undergoing IVF meets with their clinical team, who weigh your age, history, and goals.
Why This Matters in Embryo Donation
Genetic testing comes up often in embryo donation. Some embryos available for donation have already undergone PGT-A, and their results may be part of the information shared with recipients. Understanding what those results do and do not tell you can help you ask good questions and feel confident in your decisions. Many embryos are not tested, and they are still very strong candidates for donation, with high live birth prospects.
If you have questions about the testing done on specific embryos, your clinic's embryology team is the best source for those details. And if you are exploring embryo donation and want to understand your options, the team at Embryo Connections is here to walk alongside you.