Skip to main content

You have chosen not to allow videos from the 3rd party streaming service (YouTube), if you would like to see these videos, please change your Privacy policy and cookie settings.

The HFEA has launched its new data dashboard with data going back over 30 years. Access it here.

Pre-implantation genetic testing for aneuploidy (PGT-A)

For most patients, having a routine cycle of proven fertility treatment is effective without using any treatment add-ons.

Our ratings indicate whether the evidence from studies shows that a treatment add-on is effective at improving treatment outcomes for someone undergoing fertility treatment. Our ratings do not tell you how much that treatment add-on improves your chances of having a baby – please discuss this with your clinic.

What is PGT-A?

PGT-A (previously known as preimplantation genetic screening or PGS) involves checking embryos for abnormalities in the number of chromosomes. Embryos with missing or extra chromosomes (known as aneuploid embryos) have less chance of developing into a baby or, less commonly, may result in a baby being born with a genetic condition. Embryos with the correct chromosome number are known as euploid. PGT-A is therefore offered to some patients as a treatment to help identify euploid embryos and avoid transferring aneuploid embryos.

To perform PGT-A, embryologists remove a cell, or if at a later stage, several cells (a biopsy), from the embryo, which are then tested to assess the number of chromosomes they contain. The biopsy result is used to reflect the embryo as a whole. The embryo can still develop with fewer cells, if the removal of cells is done carefully.

Sometimes, the result is reported as mosaic, which means the embryo contains both euploids and aneuploid cells. The proportion of euploid and aneuploid cells can impact the chance of successful outcome if the embryo is transferred. Mosaic embryos may have a lower chance of pregnancy but there are reports of healthy live births after a transfer of a mosaic embryo. There are concerns that mosaic embryos may be discarded if PGT-A analysis looks at only the portion of cells from the embryo that all happen to be aneuploid, when they also contain normal cells and may be able to result in a live birth. Clinics may have different practices regarding testing, reporting and transfer of embryos reported as mosaic so it is important to discuss this with your clinic.

Find out more about PGT-A

Find out more about blastocyst embryos

Ratings for PGT-A
Rated red for increasing chances of having a baby for most fertility patients
Red traffic light
For most fertility patients, the use of PGT-A is rated red for improving the chances of having a baby. This is because PGT-A is a selection tool that often reduces the number of embryos available for transfer. In addition the time to conception resulting in live birth may also be longer.
See the sections What’s the evidence for PGT-A? and Is this treatment add-on safe? for more information.
Rated green for reducing the chances of miscarriage for most fertility patients
Green traffic light
On balance, findings from high quality evidence shows this add-on is effective at reducing the chances of miscarriage for most fertility patients. PGT-A can be considered where appropriate on an individual basis depending on a patient's personal circumstances and medical history.
This does not remove the chance of having a miscarriage entirely, as there are other reasons a miscarriage may occur other than aneuploidy. The NHS page on miscarriage has further information on this.
Reducing the chance of miscarriage may also not increase your chance of having a baby and using PGT-A may decrease the chance of having a baby. See the sections What’s the evidence for PGT-A? and Is this treatment add-on safe? for more information.
Rated grey for reducing the chances of miscarriage for older women
Grey traffic light
The use of PGT-A is rated grey for reducing the chances of miscarriage in older women. This is because there is insufficient moderate/high quality evidence investigating the effectiveness of using PGT-A in older women.
Rated grey for improving chances of having a baby for older women
Grey traffic light
The use of PGT-A is rated grey for improving the chances of having a baby in older women. This is because there is insufficient moderate/high quality evidence investigating the effectiveness of using PGT-A in older women.

Specific safety concerns about a treatment add-on are included under the dedicated section Is this treatment add-on safe?

What do ratings mean?

There are five ratings that indicate whether a treatment add-on is effective at improving treatment outcomes for someone undergoing fertility treatment, according to the evidence from studies. To make it easier to understand the scientific evidence for each treatment add-on we have a range of symbols and colours for each rated add-on below.

Green traffic light

On balance, findings from high quality evidence shows this add-on is effective at improving the treatment outcome.

Yellow traffic light

On balance, it is not clear whether this add-on is effective at improving the treatment outcome. This is because there is conflicting moderate/high quality evidence – in some studies the add-on has been found to be effective, but in other studies it has not.

Grey traffic light

We cannot rate the effectiveness of this add-on at improving the treatment outcome as there is insufficient moderate/high quality evidence.

Black traffic light

On balance, the findings from moderate/high quality evidence shows that this add-on has no effect on the treatment outcome.

Red traffic light

There are potential safety concerns and/or, on balance, findings from moderate/high quality evidence shows that this add-on may reduce treatment effectiveness.

All treatment add-ons on our list will have a rating to indicate whether the evidence shows that the treatment add-on is effective at improving the chances of having a baby for most fertility patients. Some treatment add-ons on our list may also have additional ratings for specific treatment outcomes. For example, whether the evidence shows that the treatment add-on reduces miscarriage. There may also be further ratings for specific patient groups, for example whether the evidence shows that the treatment add-on is effective for those who are aged over 40. Please see the individual webpages for each treatment add-on for their ratings.

An agreement between the HFEA and other professional and patient bodies (the 19th October 2023 consensus statement) states that treatments that have no strong evidence of their safety and/or effectiveness should only be offered in a research setting. Patients should not be charged extra to take part in research, including clinical trials.

What’s the evidence for PGT-A?

PGT-A is now mostly carried out at the blastocyst stage on day five or six. There is no evidence from randomised controlled trials (RCTs) that PGT-A carried out at this stage is effective at improving your chances of having a baby for most patients undergoing IVF. As it is a selection tool, PGT-A often reduces the number of embryos available for transfer.

There is some evidence that suggests PGT-A may be beneficial for reducing the rate of miscarriage. The evidence that PGT-A can reduce the rate of miscarriage in certain groups of women, particularly older women or women with a history of miscarriage, is a secondary outcome, meaning it was not the main aim of this research, so the study was not designed to investigate the effect of PGT-A on miscarriage rate, which may make these secondary results less reliable. For this reason, it is important to discuss your individual circumstances with your doctor. It is important to keep in mind that this reduction in the rate of miscarriage does not remove the chance of having a miscarriage entirely, as there are other reasons this may occur other than aneuploidy. The NHS page on miscarriage has further information on this. Reducing the chance of miscarriage may also not increase your chance of having a baby and using PGT-A may decrease the chance of having a baby as it often reduces the number of embryos available for transfer.

For some patients, PGT-A may shorten the time to pregnancy (by avoiding a series of embryo transfers). However, the evidence shows that the time to achieving pregnancy for most patients may be longer due to the additional time taken to carry out this test.

At the October 2019 and July 2023 Scientific and Clinical Advances Advisory Committee (SCAAC) meetings the Committee evaluated the evidence base for PGT-A. Minutes of these discussions and the evidence used to inform them are available on the SCAAC webpage.

This Cochrane review has further information on the evidence for PGT-A.

Is this treatment add-on safe?

PGT-A does not carry any additional known risks for the person undergoing fertility treatment. However, PGT-A is known to carry some risks for the embryo:

  • Although current PGT-A techniques are mostly very accurate, the test may give the wrong result (it may miss an abnormality or detect one that isn’t there).
  • if a test result is not accurate, healthy embryos may be discarded, meaning you may have fewer embryos for transfer.
  • In some cases viable embryos could be discarded. This is because not all embryos may be suitable for biopsy, or because embryos are reported as mosaic. Mosaic embryos may have a lower chance of pregnancy but there are reports of healthy live births after a transfer of a mosaic embryo.
  • It is also possible that no embryos may be suitable if chromosomal abnormalities are detected in all the embryos tested. This would mean that although PGT-A can reduce the chances of miscarriage, it may not translate to an increased chance in having a baby.
  • Embryos can continue to develop successfully after a few cells have been removed, however, removing cells from the embryo may damage it and prevent it from successfully developing.

If you have any questions about the safety and risks, your clinic will be able to discuss whether a treatment add-on would be safe for you to use considering your specific medical history and circumstances.

Studies reviewed for this treatment add-on

The HFEA have reviewed the following studies for PGT-A:

Mastenbroek 2007 NEJM 2007;357:9-17.
Hardarson 2008 10.1093/humrep/den217
Staessen 2008 10.1093/humrep/den367
Blockeel 2008 RBMO 2008;17(6):848-54.
Meyer 2009 10.1016/j.fertnstert.2008.02.162
Schoolcraft 2009 10.1016/j.fertnstert.2008.05.029
Sher 2009 10.1016/j.fertnstert.2008.11.029
Debrock 2010 10.1016/jfertnstert.2008.10.072
Ikuma 2015 10.1371/journal.pone.0129958
Rubio 2017 10.1016/j.fertnstert.2017.03.011
Yang 2012 Molec Cytogen 2012;5:24
Forman 2013 10.1016/j.fertnstert.2013.02.056
Scott 2013 10.1016/j.fertnstert.2013.04.035
Ozgur 2019 10.1007/s10815-018-01399-1
Munné 2019 10.1016/j.fertnstert.2019.07.1346
Cimadomo 2019 10.1093/humrep/dez078
Yan 2021 10.1056/NEJMoa2103613
De Munck 2022 10.1371/journal.pone.0267241
Idárraga 2022 10.5935/1518-0557.20210085
Ubaldi 2017 10.1016/j.fertnstert.2017.03.007
Verpoest 2018 10.1093/humrep/dey262

What are treatment add-ons?

In vitro fertilisation (IVF) and intrauterine insemination (IUI) are established treatments that have been proven effective for most patients. Treatment add-ons are optional non-essential treatments that may be offered in addition to such proven fertility treatment. The HFEA provides information on add-ons that meet the following criteria:

  • Additional treatments (to the core treatment e.g. IVF or IUI), that are being offered to the general patient population in licensed fertility clinics in the UK,
  • Where there are published scientific studies which claim to demonstrate that the treatment add-on improves the chances of having a baby or other treatment outcomes rated by the HFEA; but
  • where evidence of effectiveness for the use of the treatment in a clinical setting is lacking or absent; and
  • where patients need unbiased information about the effectiveness and risks of this treatment.

It is important to keep in mind that for most patients, having a routine cycle of proven fertility treatment is effective without using any treatment add-ons. If you are paying directly for your own treatment, you may want to think about whether it might be more effective and/or affordable to pay for multiple routine proven treatment cycles, rather than spending large sums of money on a single treatment cycle with treatment add-ons that haven’t been proven to be effective at increasing the likelihood of you having a baby.

We aim to publish clear and reliable information about some of the treatment add-ons that don’t have enough evidence to show that they are effective at improving your chances of having a baby and other relevant treatment outcomes. This provides useful information to patients and allows them to question the use of add-ons

Review date: 19 October 2025