PGT-A

PGT-A is preimplantation genetic testing for aneuploidy. A few cells are biopsied from the outer layer of a blastocyst and checked for the right number of chromosomes, so that embryos with the wrong count are not transferred. Its value is still debated, with good arguments on both sides, and it suits some people much more than others.

Where you'll meet it

At the point where the plan for a cycle is being written, because it has to be decided before egg collection rather than after. It is offered routinely in some clinics and rarely in others, so it is worth asking how the advice relates to your own results.

What the test does

A large share of embryos that fail do so because the chromosome count is wrong. That happens more often as the egg ages, and it is the main reason live birth rates fall with age. An aneuploid embryo usually either fails to implant or miscarries.

PGT-A tries to identify those before transfer. On day five or six, an embryologist removes a handful of cells from the trophectoderm, the outer layer that would become the placenta, and the embryo is frozen while the sample is analysed. Results come back over the following weeks, and a frozen transfer follows with an embryo that tested normal.

In practice, testing turns every cycle into a freeze-all cycle, adds a laboratory fee per embryo plus a biopsy fee, and delays the transfer.

The case for it

Where it clearly helps is in avoiding transfers that were never going to work. If you have several blastocysts and are choosing between them, testing can put the ones with a normal count first, which can mean fewer failed transfers and fewer miscarriages on the way to the same outcome. For older patients, and for people who have had repeated losses, that is a real and humane benefit. Fewer negative pregnancy tests is worth something even if the end result is unchanged.

The case against it

What good trials have struggled to show is that PGT-A produces more babies per cycle started. It reorders the queue rather than adding to it. If your embryos were going to give you one baby between them, testing tells you which one faster; it does not create a second.

Then there is the accuracy problem. The biopsy samples the part that becomes the placenta, not the part that becomes the baby, and embryos can be mosaic, with a mix of normal and abnormal cells. So a result can mislead in both directions. Embryos labelled abnormal or mosaic have gone on to produce healthy children when transferred, which is why the reporting language shifted and why some clinics will now discuss transferring a mosaic embryo rather than discarding it.

That matters most for younger patients with few embryos, where setting aside an embryo that would have worked could cost a cycle. The biopsy itself carries a small risk, which appears minimal in experienced hands.

What it is not

PGT-A is not the same as PGT-M or PGT-SR, which test for a specific inherited condition or a known chromosome rearrangement in a parent. Those have a clear indication, a defined question and a very different evidence base. If someone in the family carries a serious genetic condition, that is a genetics referral rather than an add-on conversation.

PGT-A is also not a guarantee of a healthy baby, and it does not replace the screening offered in pregnancy.

Questions to ask

Ask what testing would change about your plan, not what it might reveal. Ask how many embryos they expect you to have, because with one or two the case is weakest. Ask what the clinic does with a mosaic result and whether they would discuss transferring one. Ask the total extra cost including the biopsy, the per-embryo fee, the freezing and the separate transfer. And ask what the trial evidence shows for someone your age; a clinic that answers that precisely is one you can trust.

The PGT-A guide covers the evidence, the process and the cost in full.

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