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Frequently asked questions about Pre-implantation genetic testing for aneuploidy (PGT-A)

What is PGT-A?

PGT-A (previously known as preimplantation genetic screening or PGS) is a treatment add-on. It involves checking embryos created by in vitro fertilisation (IVF) or intracytoplasmic sperm injection (ICSI) for abnormalities in the number of chromosomes. PGT-A doesn’t check for specific genetic diagnoses.

During PGT-A, a single cell or a small number of cells is removed from the embryo. The DNA of these cells is then tested to see whether they have any chromosomal abnormalities. Only embryos without chromosomal abnormalities are placed back in the womb.

Who might be recommended to have PGT-A?

Older women are more likely to have eggs with the wrong number of chromosomes, so traditionally it’s been offered to women over 37. Abnormal chromosomes are thought to be the main reason why older women have difficulties conceiving and are more likely to have a miscarriage or a baby with Down’s Syndrome.

Your doctor may also recommend PGT-A if you have a family history of chromosome problems, if your sperm is at risk of carrying abnormal chromosomes, or if you’ve had several miscarriages or failed IVF attempts without explanation.

However, there is limited evidence to show that PGT-A benefits these groups (see more below). It’s also not a guaranteed way to prevent miscarriage or to have a baby.

What causes abnormal chromosomes?

When the cells of eggs, sperm and embryos divide this can lead to too many, or too few, chromosomes, or with missing or added pieces of DNA. Abnormal chromosomes happen very frequently during the normal production of eggs, sperm and during embryo development.

Does PGT-A work?

PGT-A is traditionally offered to women over 37 with a history of miscarriage or failed IVF cycles or people with a family history of chromosome problems. However, to date there is little evidence showing it improves the chances of having a baby for most fertility patients and therefore it is considered a treatment add-on.

Find out more about PGT-A on our treatment add-ons page

Until larger trials have been run and we have more evidence, there’s no guarantee that PGT-A can improve your chances of a successful pregnancy.


There’s a risk of misdiagnosing a healthy embryo

How safe is it for the embryos?

PGT-A involves taking a biopsy, to remove a cell or number of cells, from an embryo which can sometimes cause damage to the embryo and prevent it from developing once it has been transferred into the womb.

Are there any other risks?

PGT-A carries the same risks as IVF – find out more about the risks of fertility treatment.

However, PGT-A also has some treatment-specific risks. This includes the possibility of a misdiagnosis (eg due to mosaicism described above). There is also the risk that, if all the embryos are found to have abnormal chromosomes, there won’t be any embryos to put back in the womb. This is especially likely for older women.

Can I have PGT-A on the NHS?

No, PGT-A is not currently funded by the NHS. PGT-A can be expensive so you should talk to your clinic about likely costs and make sure your clinician clearly explains why PGT-A might be appropriate for you. 

Review date: 1 September 2025