PGT-A and embryo screening: Who it may suit and what to consider

Whether PGT-A embryo screening is worth considering depends on factors such as your age, fertility history, previous miscarriages or IVF cycles, and the number of embryos available. Your fertility specialist at London Women’s Clinic can review these factors with you and explain the potential benefits and limitations before you decide whether to include embryo screening in your treatment.

Book a consultation to discuss whether PGT-A may be relevant to your IVF treatment.

What is PGT-A embryo screening?

PGT-A stands for Preimplantation Genetic Testing for Aneuploidy. It is a type of embryo screening used with IVF to check whether an embryo has the expected number of chromosomes. An embryo with the expected number is described as euploid, while an embryo with missing or extra chromosomes is known as aneuploid. Aneuploid embryos have been shown to be  very  unlikely to result in an ongoing pregnancy and can be associated with miscarriage or, less commonly, certain genetic conditions.

PGT-A is carried out on embryos created through IVF. Once suitable embryos reach the blastocyst stage, an embryologist takes a small sample of cells, known as an embryo biopsy, which is sent for genetic analysis. We explain how this fits into your treatment cycle below.

PGT-A looks specifically at chromosome number and is different from PGT-M, which is used where there is a known risk of passing on a particular inherited single-gene condition.

Learn more about how embryo genetic testing works at London Women’s Clinic.

How PGT-A fits into an IVF cycle

PGT-A is an embryo screening test that can be added to an IVF cycle where there is a clinical reason to consider testing. Following ovarian stimulation and egg collection, mature eggs are fertilised in the laboratory and any resulting embryos are cultured for several days. Those that develop to the blastocyst stage and are suitable for testing can then undergo an embryo biopsy.

During the biopsy, an embryologist carefully removes a small number of cells from the part of the blastocyst that will go on to form the placenta. The sample is sent to a specialist genetics laboratory, where the chromosomes are analysed to identify whether the embryo is likely to be euploid, aneuploid or, in some cases, mosaic.

Because the results are not available immediately, biopsied embryos are frozen and stored while testing takes place. Your fertility specialist and embryology team will review the results with you before discussing which embryo or embryos may be suitable to consider for transfer. If you proceed, a euploid embryo can be thawed and transferred during a later frozen embryo transfer (FET) cycle.

PGT-A adds an additional step to IVF and does not guarantee that an embryo will be suitable for transfer or that a transfer will result in pregnancy. Your clinical team will explain how testing could affect the timing of your treatment and the number of embryos available before you decide whether to proceed.

Who may be offered PGT-A?

PGT-A is not routinely recommended for everyone having IVF. Your fertility specialist may discuss it with you when your age, treatment history or expected embryo numbers suggest that information about chromosome number could be useful when planning which embryo to transfer.

This may include:

• Patients in their late 30s or 40s: Chromosomal abnormalities in embryos become more common as the age of the person providing the eggs increases. PGT-A may therefore be discussed with patients over 37 and as part of fertility treatment over 40, although age alone does not mean that testing will be recommended.
• People who have experienced recurrent miscarriage: many miscarriages are caused by chromosomal abnormalities in the embryo. Testing may help identify euploid embryos for transfer, but it cannot identify or prevent every cause of miscarriage.
• People who have had previous unsuccessful IVF cycles: If embryo transfers have not resulted in an ongoing pregnancy, your specialist may discuss whether PGT-A could help inform the next transfer. Previous failed IVF does not, however, mean that PGT-A will necessarily improve the chance of having a baby.
• Patients with several embryos suitable for testing: When there are multiple suitable blastocysts to choose from, chromosome information may provide another factor to consider alongside embryo development and grading when deciding which to prioritise for transfer.
• Patients who wish to avoid investing time in a pregnancy likely to end in miscarriage. This may be of particular value in women above 40.
• Whether PGT-A is worth considering also depends on factors such as ovarian reserve, the number of embryos you are likely to create, your previous cycle outcomes and the importance of not losing time to conceive an ongoing pregnancy.  Testing can reduce or in some circumstances increase  the number of embryos available for transfer, so the potential value of gaining this information needs to be weighed against its limitations for your individual circumstances

A practical decision guide

There is no single test result, age or treatment history that determines whether you should have PGT-A. Instead, your fertility specialist will consider several factors together when discussing whether embryo screening could help with decisions during your IVF cycle.

• What do your age and ovarian reserve suggest? Age and ovarian reserve provide different information when planning treatment. Age can influence the likelihood of embryo aneuploidy, while ovarian reserve helps indicate how you may respond to stimulation and how many eggs might be collected. Together with your wider fertility history, this can help your specialist assess whether there are likely to be enough suitable embryos for PGT-A to provide meaningful information.
• How many embryos are available for testing? PGT-A can be of particular value when there are several suitable blastocysts to choose between. If only a small number are expected, your specialist can talk through whether testing is likely to add enough value to justify the additional step involved.
• Have you experienced recurrent miscarriage? Chromosomal abnormalities in an embryo can cause miscarriage, so your history may prompt a conversation about PGT-A. However, there are other reasons why pregnancy loss can occur and embryo screening cannot identify them all.
• What happened during previous IVF treatment? Your specialist will look at factors such as embryo development, grading, previous transfer outcomes and any pregnancies following treatment. This wider picture can help determine whether chromosome testing could inform decisions before another cycle or transfer.
• Is there a known genetic condition in your family? If you are concerned about passing on a specific inherited condition, PGT-A may not be the test you need. PGT-M is designed to test for particular single-gene conditions, and your clinical team can advise which form of embryo genetic testing is relevant.

Your priorities matter too. Before making a decision, your specialist can help you weigh the information PGT-A might provide against its limitations, your previous treatment outcomes, embryo development and grading, and the number of embryos.

Can PGT-A reduce miscarriage risk?

Chromosomal abnormalities are a common cause of miscarriage, particularly as the age of the person providing the eggs increases. An aneuploid embryo has missing or extra chromosomes, which can prevent it from developing normally and may result in implantation failure or pregnancy loss.

PGT-A can identify embryos that are likely to be aneuploid before transfer, allowing the clinical team to prioritise embryos with the expected number of chromosomes. For some patients, this may reduce the risk of miscarriage following an embryo transfer.

PGT-A cannot prevent all miscarriages. Pregnancy loss can happen for reasons unrelated to embryo chromosome number, and a euploid PGT-A result cannot guarantee that an embryo will implant or that a pregnancy will continue.

If you have experienced recurrent miscarriage, your fertility specialist can review your history and any previous IVF or pregnancy outcomes before discussing whether PGT-A has a role in your treatment. This also helps identify whether other investigations or factors need to be considered rather than assuming chromosome screening alone will provide the answer.

What PGT-A can tell you

PGT-A provides information about the number of chromosomes in the cells sampled from an embryo. The results can indicate whether an embryo is likely to be:

• Euploid: all the cells tested have the expected number of chromosomes.
• Aneuploid: all the cells tested have missing or extra chromosomes.
• Mosaic: the sample contains a mixture of cells with expected and unexpected chromosome numbers. These results require careful interpretation with your clinical team.

This information can help your fertility specialist and embryology team decide which embryos to prioritise for transfer, particularly when you have several suitable blastocysts available. For example, when planning a frozen embryo transfer, PGT-A results can be considered alongside factors such as embryo development and grading.

PGT-A can therefore help with embryo selection, but the result needs to be considered as one part of the wider clinical picture rather than a prediction of whether an individual embryo will result in a baby.

What PGT-A cannot tell you

PGT-A looks specifically at chromosome number in the cells taken during the embryo biopsy. It does not provide a complete assessment of an embryo's health, genetics or future development.

In particular, PGT-A cannot:

• guarantee that an embryo will implant after transfer
• guarantee a pregnancy or live birth
• predict every aspect of a future child's health
• detect every genetic condition or inherited disorder
• identify every possible cause of miscarriage
• guarantee that a pregnancy will not end in miscarriage

A euploid result therefore does not mean an embryo is certain to result in a healthy pregnancy or baby. Similarly, PGT-A is different from testing for a known inherited condition; where this is the concern, your specialist may discuss whether PGT-M or another form of embryo genetic testing is relevant instead.

Benefits and limitations of PGT-A

Mosaic or inconclusive results can also require further specialist interpretation. Your fertility specialist can talk through what different outcomes could mean, alongside the potential benefits and limitations of testing in relation to your individual circumstances.

PGT-A and PGT-M: what is the difference?

PGT-A and PGT-M are both forms of embryo genetic testing used alongside IVF, but they look for different things.

PGT-A assesses the number of chromosomes in cells sampled from an embryo. It can identify embryos that are likely to have the expected number of chromosomes, as well as those with missing or extra chromosomes.

PGT-M (preimplantation genetic testing for monogenic disorders) has a different purpose. It is used when there is a known risk of passing on a specific inherited condition caused by a change in a single gene. Testing is designed around the particular condition involved, so it requires specialist assessment and preparation before an IVF cycle begins.

If you or your partner have a known genetic condition, are carriers of one, or have concerns about your family history, your fertility specialist can advise whether PGT-M or another form of genetic testing should be explored rather than PGT-A.

Questions to discuss with your fertility specialist

Choosing whether to include PGT-A in your IVF cycle should involve a conversation about what the test could add in your individual circumstances. It can be useful to ask:

●     How does my age affect the likelihood of creating euploid and aneuploid embryos?

●     What do my AMH level and ovarian reserve suggest about how I might respond to IVF stimulation?

●     How many eggs and blastocysts might we reasonably expect from my treatment?

●     If only a small number of embryos are available, how could this affect the value of PGT-A for me?

●     Could chromosome abnormalities have played a role in my previous miscarriages, and are there other possible causes we should investigate?

●     What can we learn from my previous IVF cycles, including embryo development, grading and transfer outcomes?

●     How would PGT-A results influence which embryo you recommend transferring first?

●     What happens if testing identifies no euploid embryos?

●     What would a mosaic or inconclusive result mean, and how would you advise us about the options available?

●     How could PGT-A affect the timing of my treatment and plans for a frozen embryo transfer?

●     What are the limitations or risks of testing in my particular circumstances?

●     Would PGT-A provide information that is useful to my treatment decisions, or would proceeding without testing also be a reasonable option?

Your fertility specialist can consider these questions together rather than relying on any one factor to determine whether PGT-A is suitable. This gives you the opportunity to understand what different results could mean before deciding whether embryo screening should form part of your IVF treatment.

Next steps with London Women’s Clinic

If you’re considering PGT-A, the next step is to discuss it with a fertility specialist in the context of your own treatment. Your team at London Women’s Clinic will review factors such as your age, ovarian reserve, previous pregnancies or IVF cycles and the number of embryos you may have available, before talking through what PGT-A could — and could not — add to your treatment.

You can learn more about embryo genetic testing, including our dedicated information on PGT-A, or explore how testing may fit alongside IVF treatment. If age is an important consideration, our fertility treatment for over-40s page provides further information about your options.

Book a consultation with a London Women’s Clinic fertility specialist to review your circumstances and discuss whether PGT-A has a role in your treatment.

PGT-A and embryo screening FAQs

Is PGT-A the same as embryo screening?

Embryo screening is a broader, patient-friendly term that is often used when talking about PGT-A. More specifically, PGT-A is a test that looks at the number of chromosomes in cells sampled from an embryo to identify whether there are missing or extra chromosomes. It does not screen for every possible genetic condition or aspect of embryo health.

Can PGT-A reduce miscarriage risk?

It may reduce the risk of miscarriage for some patients by helping the clinical team avoid transferring embryos identified as aneuploid, as chromosomal abnormalities are one possible cause of pregnancy loss. However, miscarriage can happen for many other reasons, so PGT-A cannot remove the risk completely.

Does PGT-A increase my chance of having a baby?

If patients plan to transfer all embryos available, the HFEA considers that current evidence does not show that PGT-A increases the overall chance of having a baby. The HFEA therefore recommends considering the evidence, possible risks and your individual circumstances when deciding whether to add PGT-A to treatment. Your fertility specialist can explain how this evidence relates to you.

Who is most likely to discuss PGT-A with a doctor?

PGT-A may come up in conversations with patients in their late 30s or 40s, those who have experienced recurrent miscarriage or previous unsuccessful IVF treatment, and people with several embryos available for selection. These factors do not automatically mean PGT-A is recommended, and your wider fertility history and expected embryo numbers also need to be taken into account.

Can PGT-A test for every genetic condition?

No. PGT-A assesses chromosome number rather than testing for every genetic condition. If you have a known risk of passing on a particular inherited single-gene condition, PGT-M may be more relevant. Your clinical team can advise which type of embryo genetic testing applies to your circumstances.

What happens if all embryos are abnormal?

If all embryos tested are reported as aneuploid, there may be no embryo recommended for transfer from that group. Your clinical team will review the results with you before any decisions are made, including whether there are mosaic or inconclusive findings that need further interpretation and what options may be available next.

What does a mosaic embryo result mean?

A mosaic result means that the biopsy sample contains a mixture of cells with the expected number of chromosomes and cells with chromosome abnormalities. Mosaic results require careful interpretation, so specialist review and counselling are important before making decisions about embryo transfer. Your clinical team can explain the particular result and discuss whether transfer may be considered in your circumstances.

Do I need PGT-A if I am under 35?

Not necessarily. PGT-A is generally discussed less often with younger patients, but age alone doesn't determine whether testing has a role in your treatment. Your fertility history, previous pregnancies or IVF cycles and the number of embryos expected or available can all form part of the decision.

References / Further reading

Pre-implantation genetic testing for aneuploidy (PGT-A) | HFEA (2023)

Treatment add-ons with limited evidence | HFEA (2023)

Fertility problems: assessment and treatment | Guidance | NICE (2026)