PGT-A: what genetic testing of embryos really promises

During an IVF cycle, embryos grow to day five or six, the blastocyst stage. If PGT-A is chosen, a few cells are taken from the part that will form the placenta, not from the embryo itself, and the number of chromosomes is analysed. Embryos with a normal number are called euploid, those with an abnormal number aneuploid. Aneuploidy is the most common reason an embryo fails to implant or an early miscarriage happens, and it rises with the age of the egg.

The idea is that transferring a euploid embryo raises the chance per transfer and lowers the risk of miscarriage. But it is important to understand that PGT-A does not change the embryo; it only provides information to choose among those you already have. If you have a single embryo, the information may be useful, but it does not create a second one.

The benefit of PGT-A is clearest in some situations. In women over 37–38, where the proportion of aneuploid embryos is higher, testing can avoid transfers that would not succeed and shorten the time to a pregnancy. In couples with recurrent miscarriage or repeated failed transfers, it can offer an explanation and change the strategy. When there are enough embryos to have a choice, the information becomes practically useful.

The benefit is less clear in young women with good-quality embryos, where most embryos are expected to be normal, and in those with very few embryos, where there is nothing to choose between. In these cases PGT-A can add cost and a small risk without raising the overall chance of pregnancy.

No test is perfect. There is a small margin of error, and some embryos give 'mosaic' results, where normal and abnormal cells are found together. These results are hard to interpret and some mosaic embryos have led to healthy pregnancies; no embryo is therefore discarded on a label alone without a careful conversation.

There is also a very small theoretical risk from the biopsy itself, and the fact that the test analyses the forming placenta, not the embryo directly. For these reasons PGT-A is considered a helpful tool, not a guarantee. It reduces uncertainty but does not eliminate it, and it does not change the number of embryos you have in hand.

The decision about PGT-A is made together, taking into account your age, the expected number of embryos, the history of miscarriage or failed transfers, and your expectations. It is not a compulsory step of every IVF cycle and it is not a sign of 'better' treatment; it is a choice that makes sense for some situations and not others.

What helps most is an honest conversation explaining what you will and will not learn, how many embryos are expected, and how the plan changes if the result is one thing or another. The aim is to make an informed decision, not to feel you are leaving something behind if you choose not to do it.