PGT-A counts the chromosomes in an embryo. PGT-M looks for one specific inherited condition that you already know runs in your family.
If you or your partner carry a serious genetic condition, PGT-M is the test designed for you. If you have no known genetic condition but have faced repeated miscarriages or failed transfers, a clinic may raise PGT-A, although the evidence for it is more mixed.
This guide explains how each test works, who it suits and where its limits lie. If you would like to talk through your own situation first, you can book a free fertility advisory call or read about our embryo genetic testing.
PGT-A vs PGT-M: What Is the Difference?
PGT stands for preimplantation genetic testing. In both versions, an embryologist removes a few cells from an embryo during IVF, a laboratory analyses them, and the results help you and your doctor choose which embryo to transfer.
The difference between PGT-A and PGT-M is the target of the analysis. PGT-A screens for aneuploidy, which means an embryo has an extra or missing chromosome. A typical embryo has 46 chromosomes, 23 from each parent. PGT-M instead looks for a single gene change behind a monogenic disorder, meaning a condition caused by one gene, such as cystic fibrosis.
| Feature | PGT-A | PGT-M |
|---|---|---|
| Full name | Preimplantation genetic testing for aneuploidy | Preimplantation genetic testing for monogenic disorders |
| What it checks | Chromosome number | One specific gene change |
| Main purpose | Choose embryos with the expected chromosome count | Avoid passing on a known inherited condition |
| Who it suits | Selected fertility patients, case by case | Carriers or couples with a family history of a serious condition |
| Preparation | None beyond IVF planning | Family-specific test design before the cycle |
| Regulator involvement | Rated by the HFEA as an add-on | HFEA must approve the condition |
How Does PGT-A Testing Work?
PGT-A works by biopsying a blastocyst, which is an embryo that has developed for five to six days, and counting its chromosomes.
Your cycle begins as usual, with ovarian stimulation and egg collection. After fertilisation, the embryos grow in the laboratory. On day five or six, an embryologist removes a few cells from the outer layer of each blastocyst. That layer forms the placenta, so the sample comes from a different part of the embryo than the one that becomes the baby. The embryo is then frozen while a specialist laboratory counts the chromosomes, usually by next-generation sequencing, a method that reads DNA in detail.
Once results arrive, a specialist can thaw and transfer an embryo with the expected chromosome count in a later cycle. At IVF Matters, results can take three to four weeks, as stated on our PGT page. Our guide to PGT-A testing explains the process in more detail.
Why Is PGT-A Testing Done?
Clinics offer PGT-A because embryos with an abnormal chromosome count are a common reason for failed implantation and miscarriage, and the share of such embryos rises with the age of the egg provider. The idea is to avoid transferring an embryo that was unlikely to continue.
It is usually discussed for patients with recurrent miscarriage, several failed transfers or an age over 35. For example, a patient aged 39 with two failed transfers might be offered PGT-A so that each later transfer uses an embryo with the expected chromosome count.
The HFEA rates PGT-A red for improving the chance of having a baby for most patients, because it is a selection tool that often reduces the number of embryos available for transfer. Testing can therefore leave you with fewer embryos to use. The HFEA rates PGT-A green for reducing miscarriage in most patients, and grey for older women, where it cannot rate the effect. The HFEA page on PGT-A has the full ratings, and the HFEA guide to treatment add-ons explains what each colour means.
Who Should Consider PGT-M?
You should consider PGT-M if you or your partner carry a serious inherited condition and want to avoid passing it on. It is not a general screening test, and it only works for a condition already identified in your family.
The HFEA states that doctors may discuss it if you have previously ended a pregnancy because of a serious genetic condition, already have a child with one, or have a family history of serious genetic or chromosome problems. The chance of passing a condition on depends on how it is inherited. Genetic Alliance UK gives 1 in 4 (25%) per pregnancy for autosomal recessive and X-linked conditions, and 1 in 2 (50%) for autosomal dominant conditions.
PGT-M starts with your GP, who refers you to a Regional Clinical Genetics Service. If PGT-M is suitable, you'll be referred to an HFEA-licensed clinic for embryo testing, which may not be close to home. The HFEA must also have approved your condition, and it reports that over 2,000 genetic conditions have been approved so far. Details are on the HFEA page on PGT-M and PGT-SR.
Preparation, Timeline and Accuracy: How the Two Tests Compare
Side by side, PGT-A and PGT-M differ mainly in preparation. PGT-A slots into a standard IVF plan, whereas PGT-M needs a test built around your family's specific gene change before treatment can begin.
| Factor | PGT-A | PGT-M |
|---|---|---|
| Preparation | None beyond IVF planning | Genetic counselling and a family-specific test design |
| Typical timeline | IVF cycle plus 3 to 4 weeks for results at IVF Matters | Genetic Alliance UK gives 5 to 12 months of preparation, then a cycle of about 9 to 12 weeks |
| Accuracy | A screening test, so results are not diagnostic | Genetic Alliance UK: 98% to 99% accurate for most couples |
| Usual funding | Self funded | NHS funding possible in some cases |
The HFEA states that PGT-M is not 100% accurate, so tests may fail or give incorrect information. See Genetic Alliance UK on preimplantation genetic testing.
PGT-A vs PGT-M: Which Is Better?
A normal PGT-A result tells you the chromosome count looked as expected, but it does not rule out a single gene condition.
A PGT-M result tells you whether embryos carry your family's gene change, but it does not screen for chromosome problems unless the laboratory adds that analysis.
If you need PGT-M, it is reasonable to ask the laboratory whether chromosome analysis can be included on the same biopsy, since the answer depends on the lab and clinic.
| Your Situation | Test to Discuss |
|---|---|
| Known carrier of a serious gene condition | PGT-M |
| A child or past pregnancy affected by a gene condition | PGT-M |
| A chromosome rearrangement in you or your partner | PGT-SR |
| Recurrent miscarriage with no known gene cause | PGT-A, case by case |
| Several failed transfers of good quality embryos | PGT-A, case by case |
| A first IVF cycle with no risk factors | Usually neither |
Embryo testing adds cost and can reduce the number of embryos available, so it makes most sense where there is a clear reason for it.
Risks and Limits of Embryo Testing
The HFEA describes PGT-M as thought to be very safe, with no evidence that babies born after it have more health or developmental problems than babies born after IVF alone. It also notes that testing can sometimes damage an embryo, so that embryo may have to be discarded. Testing cannot guarantee a pregnancy or live birth, and fewer embryos than expected may reach the blastocyst stage to be tested.
Before you agree to any embryo test, ask for its HFEA rating in your situation, the total cost including freezing and storage, and how the laboratory reports mixed results.
PGT at IVF Matters
At IVF Matters, we offer PGT-A case by case after a consultation with Dr Irfana Koita, who reviews your history and discusses whether testing is likely to help. PGT-M is available when you or your partner is a known carrier of a genetic condition.
Costs form part of a personalised treatment plan, so check our treatment prices page or ask during your consultation. You can also read how IVF treatment in London works with us.
Frequently Asked Questions
What is PGT-SR?
PGT-SR tests for structural changes in chromosomes, such as segments that are deleted, duplicated or inverted. The HFEA states it is used when a person has a known structural rearrangement. A karyotype test can identify these changes.
Can I get PGT-M on the NHS?
Sometimes. The HFEA states that, in some cases, the NHS can fund PGT-M, depending on your situation and where you live. Genetic Alliance UK lists criteria for England, Scotland and Wales, including age, body mass index and smoking status. Your GP can advise.
Is the baby tested again during pregnancy?
Yes, confirmatory testing is offered. Genetic Alliance UK states that amniocentesis or chorionic villus sampling is offered after a pregnancy from PGT-M.
Can a condition that is not on the HFEA list be tested for?
Possibly. A clinic must apply to the HFEA to add a condition to the PGT-M list. The HFEA warns that the process can be lengthy and may not succeed.
Can I have PGT-M without IVF?
No. The HFEA states that both PGT-M and PGT-SR require IVF, because the embryos must be tested in a laboratory. The embryos that test free of the condition are usually frozen and transferred in a later cycle.
Conclusion
PGT-A and PGT-M answer different questions, so your genetic and fertility history should drive the decision. PGT-M addresses a known inherited condition and begins with a genetics referral through your GP. PGT-A is an optional chromosome screen with mixed evidence, so ask what the evidence says for your situation before paying.
When you are ready to plan, you can book a free fertility advisory call or arrange a private fertility consultation with IVF Matters.
Resources
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HFEA: PGT-M and PGT-SR
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HFEA: Preimplantation genetic testing for aneuploidy (PGT-A)
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HFEA: Treatment add-ons
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Genetic Alliance UK: Preimplantation genetic testing
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