Preimplantation Genetic Testing: PGT-A, PGT-M and What NICE Says

The honest picture, with numbers

Preimplantation genetic testing is not one thing, and most of the confusion around it comes from treating it as if it were. Three distinct tests share the initials.

• PGT-A screens embryos for the wrong number of chromosomes. It is offered to the general IVF population as a way of choosing which embryo to transfer.
• PGT-M tests for a specific inherited single-gene condition that is known to run in a family. The HFEA says it can be used with IVF to test for over 2,000 rare genetic conditions, including cystic fibrosis and early-onset Alzheimer's, with only unaffected embryos placed in the womb.
• PGT-P claims to score embryos for polygenic disease risk. The HFEA states that PGT-P is unlawful for use in the UK, because it does not meet the criteria for genetic testing and is not currently backed by evidence from scientific studies.

Almost every argument about "genetic testing of embryos" is really an argument about PGT-A. PGT-M is an established, regulated treatment for families with a known serious condition, accessed through approved-condition lists and clinics licensed to provide it.

What NICE decided about PGT-A

NG257 recommendation 1.48.1 is one sentence: do not offer pre-implantation genetic testing for aneuploidy as part of fertility treatment to improve live birth rates. That is a 2026 recommendation, made after an evidence review specifically on PGT-A as a treatment add-on.

Note what it does and does not say. It addresses live birth rates. It does not say the biology is wrong, or that aneuploidy does not matter, or that no one should ever have the test. It says that as a means of improving your chance of taking a baby home, the evidence does not support offering it.

Why the HFEA rates the same test red and green

The HFEA's rating for PGT-A looks contradictory until you read which outcome each rating refers to. There are four.

Red, in the HFEA's five-colour scheme, means there are potential safety concerns and/or that moderate to high quality evidence shows the add-on may reduce treatment effectiveness. Green means high quality evidence shows it is effective for that outcome. Grey means the evidence is insufficient to rate.

The mechanism behind the red rating is not mysterious. The HFEA explains that PGT-A is a selection tool that often reduces the number of embryos available for transfer, and that for most patients the time to achieving a pregnancy may be longer because of the additional time the test takes. Fewer embryos in play, more time consumed. The regulator also states directly that reducing the chance of miscarriage may not increase your chance of having a baby, and that using PGT-A may decrease it.

Mosaic results, and the risk of discarding a viable embryo

A biopsy takes cells from the outer layer of the embryo and the result is used to represent the embryo as a whole. Sometimes it comes back mosaic, meaning the sample contained both normal and abnormal cells.

The HFEA is candid about what follows. Mosaic embryos may have a lower chance of pregnancy, but there are reports of healthy live births after transfer of a mosaic embryo. It warns of the concern that mosaic embryos may be discarded when the analysis happens to sample only abnormal cells from an embryo that also contains normal ones and could have resulted in a live birth. It adds that although current techniques are mostly very accurate, the test may miss an abnormality or detect one that is not there, and that inaccurate results mean healthy embryos may be discarded.

Clinics differ in how they test, report and transfer mosaic embryos, so the HFEA advises discussing this specifically with yours. That is not a formality — a clinic's mosaic policy can change what happens to embryos you already have.

Where PGT-A is nonetheless discussed

The HFEA notes PGT-A is mostly used where women have had several miscarriages or failed IVF cycles and want to test embryos for problems that might lead to another failed treatment. NG257 does not forbid the test; it withdraws the justification of improved live birth. If reducing the chance of another miscarriage is the outcome you are trying to buy, the green rating is real and the conversation is legitimate — but the trade against a possibly lower chance of a baby has to be made explicitly, by you, in advance.

One structural point applies to every add-on in this category. The HFEA records a consensus statement, agreed in October 2023 with professional and patient bodies, that treatments without strong evidence of safety and effectiveness should only be offered in a research setting, and that patients should not be charged extra to take part in research.

What to do next

1. Establish which test is being proposed — PGT-A, PGT-M or PGT-SR. They are not interchangeable and the evidence for each is different.
2. If it is PGT-A, ask which outcome the clinic is claiming. Live birth is rated red; miscarriage reduction is rated green.
3. Ask what the clinic does with mosaic embryos, and get the policy in writing before biopsy.
4. Ask how many embryos you are likely to have. With one or two, a selection tool has almost nothing to select between.
5. Ask for the cost separately, including per-embryo biopsy and laboratory fees, and compare it with the cost of another routine cycle.
6. If a family condition is the reason, ask for genetic counselling and about PGT-M rather than PGT-A. The HFEA holds approved-condition lists and only certain clinics are licensed to offer it.

When to seek help

If you have had recurrent miscarriage or repeated implantation failure, the right first step is a diagnostic review rather than an embryo-selection product. Ask your clinic to set out what has been investigated and what has not, and to say explicitly what problem PGT-A would solve in your case. The HFEA also flags that whether embryo testing is NHS-funded depends on factors including how serious the condition is and the likelihood of a future child inheriting it, so a family history of a serious inherited condition is a reason to ask about referral and funding early rather than paying privately by default.