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PGT-A Testing: What It Is, How It Works, and Whether It’s Worth It

Pre-implantation genetic testing for aneuploidy (PGT-A) is one of the most talked-about IVF add-ons. But what does it actually tell you — and when is it worth doing?

Author

Tassia O’Callaghan

Reviewed by

Kayleigh Hartigan

15 min read

Published 28 October 2025

Spotlight:

  • PGT-A (also called PGS) screens embryos for chromosomal abnormalities before transfer.

  • It helps identify embryos with the correct number of chromosomes (euploid), which are more likely to implant and lead to a healthy pregnancy.

  • PGT-A testing is optional — it doesn’t increase egg or embryo quality but helps select the healthiest ones for transfer.

  • Results can guide single-embryo transfer decisions and may reduce miscarriage risk.

  • Costs vary, typically £2,000–£4,000 in addition to IVF treatment.

  • PGT-A isn’t offered through the NHS except in specific medical circumstances.

What do they test for in PGT-A?

PGT-A (pre-implantation genetic testing for aneuploidy) looks at the number of chromosomes inside each embryo’s cells. It checks whether an embryo has the usual 46 chromosomes (23 pairs) — known as euploid — or if any are missing or extra (aneuploidy). Embryos with an abnormal number of chromosomes are less likely to implant, may lead to miscarriage, or, more rarely, result in certain genetic conditions such as Down syndrome. [1]

PGT-A doesn’t test for specific inherited diseases or single-gene disorders — it’s purely a chromosome count test, helping clinics identify embryos most likely to develop into a healthy pregnancy.

Who is PGT-A testing for?

PGT-A testing may be suggested for some people going through IVF, but it isn’t recommended for everyone. It’s usually considered when there’s a higher chance of embryos having chromosomal abnormalities — something that can affect implantation, miscarriage risk, or pregnancy outcomes. [2]

You might be offered PGT-A if you:

  • Are over 37: As eggs are more likely to have chromosomal abnormalities with age, which can make conception harder or increase miscarriage risk.

  • Have had multiple miscarriages: Especially when no clear cause has been found.

  • Have experienced several unsuccessful IVF cycles: –Where good-quality embryos haven’t led to pregnancy.

  • Have a family history of chromosomal conditions: Such as translocations or inherited abnormalities.

  • Have concerns about sperm quality: Where there’s a known risk of chromosomal errors in the sperm.

PGT-A can help identify embryos with the right number of chromosomes, but evidence shows it doesn’t necessarily improve live birth rates for most patients. It’s best discussed with your fertility specialist to understand whether it’s appropriate for your individual situation. [1]

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How is PGT-A tested?

PGT-A testing is carried out during an IVF cycle, once embryos have developed in the lab — after fertilisation, but before embryo transfer. It’s a precise lab process designed to identify embryos with the right number of chromosomes before transfer. [3]

Here’s how it works step by step:

  1. Fertilisation and embryo growth: Eggs are retrieved, fertilised through IVF or ICSI, and grown for about 5 to 6 days until they reach the blastocyst stage.

  2. Embryo biopsy: A specialist embryologist removes a few cells from the outer layer of the embryo (the trophectoderm), which later forms the placenta. The inner cells that become the baby are left untouched.

  3. Genetic testing in the lab: The sampled cells are frozen and analysed using advanced DNA sequencing to count the number of chromosomes.

  4. Embryo grading and results: Each embryo is classified as euploid (normal), aneuploid (abnormal), or mosaic (a mix of both). Results are used to guide which embryos are most suitable for transfer in a future frozen cycle.

When performed carefully, embryos can continue developing normally after biopsy. However, because the process involves removing cells, it should always be carried out by an experienced, licensed fertility clinic.

How long does PGT-A testing take for IVF?

PGT-A testing adds a short pause to the IVF process while embryos are analysed.

After the biopsy, embryos are frozen, and results are usually ready within 1 to 2 weeks. Because the test is performed at the blastocyst stage (around day 5 or 6 after fertilisation), embryo transfer typically happens in a later frozen cycle, rather than in the same fresh cycle. This means your overall IVF timeline may extend by around 4 to 6 weeks, depending on clinic scheduling and lab turnaround times. [3]

What are the advantages of a PGT-A test?

PGT-A testing can offer some potential benefits when used in the right circumstances. While it doesn’t increase egg or embryo quality, it can help clinics identify which embryos are most likely to lead to a healthy pregnancy. [1]

  • Helps identify chromosomally normal embryos: By checking for the correct number of chromosomes, PGT-A can help select embryos with the best chance of implantation.

  • May reduce miscarriage risk: As many miscarriages are caused by chromosomal abnormalities, transferring a euploid embryo can lower this risk for some patients. [4]

  • Supports single-embryo transfer: By identifying the most viable embryo, PGT-A can reduce the need to transfer multiple embryos and lower the chance of twins or triplets. [5]

  • Can provide clarity after previous IVF failures: For people who’ve had several unsuccessful cycles, PGT-A may help uncover whether chromosomal issues are a contributing factor.

  • May shorten time to pregnancy for some patients: By prioritising embryos with the highest likelihood of success, some people may conceive in fewer transfer attempts. [6]

However, it doesn’t guarantee pregnancy — it only screens for chromosome numbers, not other genetic or developmental issues.

What are the disadvantages or risks of PGT-A?

PGT-A testing can offer valuable insights — but like any fertility treatment add-on, it comes with limitations and potential downsides to weigh up carefully. [1]

  • May not improve success rates for everyone: According to the HFEA and Cochrane evidence, there’s no strong proof that PGT-A increases live birth rates for most IVF patients. For some, it may even lower overall chances by reducing the number of embryos available for transfer. [4]

  • Risk of discarding viable embryos: Test results can sometimes misclassify embryos, especially if they’re mosaic (containing both normal and abnormal cells). This could lead to healthy embryos being excluded from transfer.

  • Can damage embryos during biopsy: Although rare with skilled embryologists, removing cells from an embryo always carries a small risk of harming its development.

  • Fewer embryos for transfer: Not all embryos are suitable for biopsy, and some may not survive the freeze–thaw process, meaning fewer options for future transfers.

  • Added cost and delay: PGT-A testing adds thousands of pounds to treatment costs and usually means embryo transfer happens in a later frozen cycle, extending the IVF timeline. [4,7]

  • Emotional and physical toll: The wait for results and the possibility of no “normal” embryos can be distressing, especially after an already demanding IVF cycle.

  • Uncertain evidence for specific groups: While it may reduce miscarriage risk in certain cases, there’s limited high-quality evidence to show clear benefit for older patients or those with recurrent IVF failure.

In short, PGT-A can help some people gain clarity — but it’s not a one-size-fits-all solution. Discussing your medical history, embryo quality, and goals with your clinic’s genetic counsellor can help determine whether it’s worth adding to your IVF plan.

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Can I ask my GP for a PGT-A test on the NHS?

No, you can’t currently get PGT-A testing through the NHS, as it’s not a funded service. This means your GP can’t directly refer you for PGT-A or arrange for it to be done within standard NHS fertility care. [2]

However, your GP can refer you to a clinical genetics service if there’s a family history of an inherited condition. In those cases, different types of testing — such as PGT-M (for single-gene disorders) or PGT-SR (for structural rearrangements) — can sometimes be NHS-funded through specialist centres like Guy’s and St Thomas’. [7,8]

If you’re interested in genetic testing as part of IVF, you’d need to go through a private fertility clinic, where PGT-A can be added to your treatment plan at an extra cost — you can browse fertility clinics to find the best clinic for you using our free Clinic Match tool.

How much does PGT-A testing cost in the UK?

Typically £2,000–£4,000 per cycle, depending on the number of embryos tested. Some clinics may offer discounted packages for multiple embryos.

Some clinics offer package deals that include biopsy and testing in one fee, while others charge per embryo. Always check what’s included in your quote, as storage and courier fees can also apply.

Understanding PGT-A results

PGT-A results can feel confusing at first, especially when you’re faced with scientific terms and uncertain outcomes. Here’s how to make sense of what your results mean — and why they’re not always black and white. [1,3,7,9]

When your embryologist reviews your embryos, they’ll usually classify them into one of three categories:

Euploid embryos (normal chromosomal number)

These embryos have the correct number of chromosomes and are most likely to implant and develop into a healthy pregnancy. Euploid embryos are typically prioritised for transfer.

However, a “normal” result doesn’t guarantee the embryo is completely free of chromosomal issues.

Aneuploid embryos (abnormal chromosomal number)

These embryos have missing or extra chromosomes, meaning they’re less likely to result in a successful pregnancy. Some aneuploid embryos fail to implant, while others can lead to miscarriage or, more rarely, genetic conditions like Down syndrome (trisomy 21).

Mosaic embryos (a mix of normal and abnormal cells)

Mosaic results fall somewhere in between. These embryos contain both euploid and aneuploid cells, and the proportion of each can influence their potential. Some mosaic embryos have led to healthy pregnancies, but they may carry a lower chance of success — and policies on transferring them differ between clinics.

It’s also worth considering that different laboratories can interpret the same embryo differently depending on how they define mosaicism thresholds.

What percentage of embryos pass PGT-A testing?

There isn’t a universal “pass rate” for embryos that undergo PGT-A, since results depend heavily on factors like age, egg and sperm quality, and embryo development. Studies show that anywhere from around 18% to 30% of embryos test as chromosomally normal (euploid), but this can drop to below 20% in patients over 40 and be much higher in younger age groups. [1,10,11,12]

Many embryos can’t be biopsied or don’t survive freezing, and around 10% of tests fail due to insufficient DNA. In short, how many embryos “pass” PGT-A varies widely — and your own results will depend on your biology and treatment response. [12]

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What happens after PGT-A testing?

After PGT-A testing, your embryos are usually frozen while you wait for the results. The testing process looks at the DNA from a few cells taken from each embryo to check whether they have the correct number of chromosomes (euploid), an abnormal number (aneuploid), or a mix of both (mosaic). Once the results are ready, your clinic will explain how many embryos are suitable for transfer. [1]

If one or more embryos are confirmed as euploid, your fertility team will usually plan a frozen embryo transfer in a future cycle. Sometimes, all embryos tested may be aneuploid or mosaic, meaning none are clearly suitable for transfer — in these cases, your doctor will talk through your options, which might include further IVF cycles or, in some situations, the transfer of a mosaic embryo after careful discussion. [3,7]

It’s important to know that while most embryos continue to develop normally after biopsy, a small number may not survive the freezing and thawing process, and occasionally the biopsy or test can fail. Your clinic will guide you through each next step, explain your individual results, and support you in deciding what comes next.

Should I PGT-A test my embryos?

Whether to do PGT-A testing is a personal choice that depends on your medical history, age, and fertility journey so far. For most people, it doesn’t increase the overall chance of having a baby — but it may help identify embryos with a lower risk of miscarriage or chromosomal issues in certain cases, like recurrent loss or older maternal age. It’s not offered on the NHS, can be expensive, and may reduce the number of embryos available for transfer. The best way to decide is to talk it through with your fertility specialist to weigh the evidence, costs, and whether it’s truly right for you. [1,2]

PGT-A testing FAQs

Does PGT-A reveal gender?

Yes, PGT-A can reveal the sex chromosomes of an embryo, which means the embryo’s sex may be known as part of the testing process. However, this information isn’t the goal of PGT-A — the test’s purpose is to check for chromosomal abnormalities, not to select for gender. [13]

Clinics have different policies on whether they disclose or use this information. Some may share an embryo’s sex if patients request it, while others may choose not to, focusing only on embryo health and quality when deciding which to transfer. It’s also considered unethical for clinics to favour one sex over another or allow non-medical sex selection.

Choosing embryos based on sex is illegal in the UK, unless it’s to avoid a serious genetic condition. [14]

Is PGT testing 100% accurate?

PGT-A testing is highly accurate — typically around 98–99% — but it’s not 100% foolproof. The test analyses a few cells from the outer layer of the embryo (the trophectoderm), which may not perfectly represent the inner cell mass that develops into the baby. Because of this, results can occasionally miss or misclassify abnormalities, especially in mosaic embryos (those containing a mix of normal and abnormal cells). [1,15,16]

Modern PGT-A techniques are reliable and continually improving, but errors can still happen — for example, a healthy embryo may be labelled abnormal, or vice versa. For that reason, if a pregnancy occurs after PGT-A, your clinic will usually recommend confirmatory prenatal testing (like CVS or amniocentesis) to verify the results. In short: PGT-A offers valuable insight, but no test can guarantee absolute accuracy or a complication-free pregnancy. [15]

Can PGT-A detect Down’s syndrome?

Yes — PGT-A can detect embryos with Down’s syndrome, because the condition is caused by having an extra copy of chromosome 21 (known as trisomy 21). PGT-A screens embryos for these kinds of chromosomal abnormalities, identifying whether they have the correct number of chromosomes before transfer. [17]

However, it’s important to know that while PGT-A can spot chromosomal differences like Down syndrome, it doesn’t diagnose the condition with complete certainty. If a PGT-A–tested embryo leads to pregnancy, prenatal testing (like NIPT, CVS, or amniocentesis) is still recommended to confirm the results. [18,19,20]

Can PGT detect spina bifida?

No, PGT-A cannot detect spina bifida. This test looks for chromosomal abnormalities — such as missing or extra chromosomes — rather than structural or developmental conditions like neural tube defects.

Spina bifida isn’t caused by aneuploidy (the kind of error PGT-A screens for), so it won’t show up in embryo testing. Instead, it’s usually identified later in pregnancy through ultrasound scans or maternal blood tests. [21]

If you have a family history of spina bifida or are taking certain medications (like valproate), your doctor may recommend high-dose folic acid before and during early pregnancy to help reduce the risk.

Can PGT-A detect all genetic disorders?

No — PGT-A can’t detect all genetic disorders. It’s designed to look for aneuploidy, meaning embryos with too many or too few chromosomes (for example, Down’s syndrome or Turner syndrome). It doesn’t identify single-gene conditions like cystic fibrosis, sickle cell anaemia, or muscular dystrophy. [17,21]

If there’s a known inherited condition in your family, your doctor may recommend a different type of test called PGT-M (for monogenic disorders) or PGT-SR (for structural rearrangements). Each test looks for specific genetic issues, so it’s important to discuss your medical and family history with your clinic to ensure the right kind of testing is used. [2,23,24]

Does PGT increase twins?

No — PGT-A doesn’t increase the chances of twins. In fact, research suggests it can reduce the risk of twin pregnancies, particularly when paired with single embryo transfer (SET). Because PGT-A identifies embryos with the best chance of developing successfully, clinics can confidently transfer just one embryo rather than two, lowering the likelihood of twins without reducing success rates. [2,25,26,27]

PGT-A also doesn’t make identical (monozygotic) twins more likely. The rate of identical twinning after IVF remains very low — similar to or only slightly above natural conception. So while IVF in general can increase the risk of multiples if multiple embryos are transferred, PGT-A is often used to help prevent that, not cause it.

Sources

  1. Human Fertilisation & Embryology Authority. Pre-implantation genetic testing for aneuploidy (PGT-A).
  2. Human Fertilisation & Embryology Authority. Frequently asked questions about Pre-implantation genetic testing for aneuploidy (PGT-A).
  3. NHS England. Preimplantation genetic testing. Last reviewed: 12/06/2023.
  4. Cornelisse, S., Zagers, M., Kostova, E., Fleischer, K., van Wely, M. and Mastenbroek, S., 2020. Preimplantation genetic testing for aneuploidies (abnormal number of chromosomes) in in vitro fertilisation. Cochrane Database of Systematic Reviews, (9).
  5. Reimundo P, Gutiérrez Romero JM, Rodríguez Pérez T, Veiga E. Single-embryo transfer: a key strategy to reduce the risk for multiple pregnancy in assisted human reproduction. Adv Lab Med. 2021 Apr 2;2(2):179-198. doi: 10.1515/almed-2021-0013. PMID: 37363329; PMCID: PMC10197809.
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  8. NHS Guy’s and St Thomas’, NHS Foundation Trust. Appointments: Pre-implantation genetic testing (PGT-M/SR). Last updated: May 2024.
  9. Bagó AC, Hernández MTI, Villarreal PC, Ortega CG, Gutiérrez AMG. The importance of standardizing criteria for PGT-A interpretation of blastocysts analyzed by next-generation sequencing. JBRA Assist Reprod. 2023 Sep 12;27(3):453-462. doi: 10.5935/1518-0557.20230011. PMID: 37579264; PMCID: PMC10712803.
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  25. Kucherov A, Fazzari M, Lieman H, Ball GD, Doody K, Jindal S. PGT-A is associated with reduced cumulative live birth rate in first reported IVF stimulation cycles age ≤ 40: an analysis of 133,494 autologous cycles reported to SART CORS. J Assist Reprod Genet. 2023 Jan;40(1):137-149. doi: 10.1007/s10815-022-02667-x. Epub 2022 Dec 1. PMID: 36454362; PMCID: PMC9840738.
  26. Kucherov A, Fazzari M, Lieman H, Ball GD, Doody K, Jindal S. PGT-A is associated with reduced cumulative live birth rate in first reported IVF stimulation cycles age ≤ 40: an analysis of 133,494 autologous cycles reported to SART CORS. J Assist Reprod Genet. 2023 Jan;40(1):137-149. doi: 10.1007/s10815-022-02667-x. Epub 2022 Dec 1. PMID: 36454362; PMCID: PMC9840738.
  27. Friedenthal, J., Maxwell, S.M., McCulloh, D.H. and Grifo, J.A., 2018. The first cut is not the deepest: preimplantation genetic testing for aneuploidy (PGT-A) does not increase monozygotic twinning and significantly decreases dizygotic twins with assisted reproductive technology (ART). Fertility and Sterility, 110(4), p.e71.