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

Treatment add-on

PGT-A for day three embryos is rated red

PGT-A for day three embryos is rated red


PGT-A for day five embryos is rated red

PGT-A for day five embryos is rated red


What does this traffic light rating mean?

The traffic light rating system consists of three colours that indicate whether the evidence, in the form of high-quality randomised control trials (RCTs), shows that a treatment add-on can safely improve the live birth rate for someone undergoing fertility treatment.

We give a red symbol for an add-on where there is no evidence to show that it can improve live birth rates. We also give a red symbol for an add-on where there is evidence to show that the add-on is unsafe.

The January 2019 consensus statement between the HFEA and 10 other professional and patient bodies agreed that treatments that have no robust 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, and should not be charged to use red-rated treatment add-ons if the reason for its use is to improve live birth rates.

For specific patient groups there may be reasons for the use of a treatment add-on other than to increase live birth rate, for example to reduce your chances of having a miscarriage. In these situations it may be appropriate for you to be offered a treatment add-on as part of your treatment and not in a research setting.

What is PGT-A?

PGT-A (also known as preimplantation genetic screening or PGS) involves checking embryos for abnormalities in the number of chromosomes. Embryos with an abnormal number of 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. PGT-A identifies aneuploid embryos that are unsuitable for fertility treatment.

To do PGT-A, embryologists remove a cell, or if at a later stage, several cells, from the embryo, which is then tested for any chromosomal abnormalities. The embryo can still develop with fewer cells, as long as the removal of cells is done carefully.

Find out more about PGT-A

Find out more about blastocyst embryos

Are there any risks?

PGT-A carries some risks:

  • 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).
  • Using PGT-A may mean you have fewer embryos to use in treatment, or for freezing to use in treatment at a later date. If any healthy embryos are erroneously discarded in this process, you may have fewer chances to transfer an embryo which could develop into a healthy baby.
  • Removing a cell from the embryo may damage it and prevent it from successfully developing once it’s been transferred to the womb.
  • Removing part of the embryo may cause changes in later growth in the womb, which may cause problems in later life.
  • In some cases, cells within the same embryo are not chromosomally identical (known as ‘mosaic’), which means that PGT-A may show that the embryo has chromosome abnormalities when in fact it’s capable of producing a normal pregnancy or vice versa. In some clinics, mosaic embryos are considered for transfer, even though they show some chromosomal abnormality.

What’s the evidence for PGT-A?

At the October 2019 Scientific and Clinical Advances Advisory Committee (SCAAC) meeting the Committee evaluated the evidence base for PGT-A. Minutes of the October 2019 discussion and the evidence used to inform this discussion are available here.

PGT-A is traditionally offered to women over 37, couples who have had several miscarriages or failed IVF cycles, people with a family history of chromosome problems, and men whose sperm may carry abnormal chromosomes. 

Up until a few years ago cells were removed from the embryo at the 8-cell stage on day 3. There is no evidence to show that this type of PGT-A is beneficial for these groups. In fact, studies have shown that this type of PGT-A can actually reduce success rates, probably because of damage to the embryo or inaccurate test results.

PGT-A is now mostly carried out at the blastocyst stage on day five or six. There is also no evidence from RCTs that PGT-A carried out at this stage increases the chances of having a baby for most patients undergoing IVF. It appears possible that reduced availability of embryos for transfer following PGT-A may counter any benefit of embryo selection.

There have been no RCTs conducted where the main objective of the study was to assess the effect of PGT-A on the rate of miscarriage. There is some evidence that suggests PGT-A may be beneficial for certain categories of women, particularly older women, in relation to a potential reduction in miscarriage. It is important to keep in mind that this reduction in the rate of miscarriage does not increase the chances of a live birth. It is likely that, with PGT-A, embryos that express a chromosomal abnormality that could lead to a miscarriage are not selected for embryo transfer. This means that although the patient does not have a miscarriage, she also does not become pregnant because the embryo transfer did not take place.

It is also important to keep in mind that the evidence that PGT-A can reduce the rate of miscarriage in certain groups of women are secondary outcomes, that is, they were not the main aim of this research. This means that 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.

Traffic light rating history

Following a decision made at the October 2019 SCAAC meeting, the traffic light rating for PGT-A for day five embryos was changed from amber to red. Minutes of the October 2019 meeting and the evidence used to inform this decision are available here.

What are treatment add-ons?

Treatment add-ons are optional additional treatments that you may be offered on top of your routine fertility treatment, often at an additional cost. Some clinics may refer to treatments add-ons as ‘supplementary’ or ‘embryology treatments’. There are a wide range of treatment add-ons on offer including tests, drugs, equipment, holistic or alternative therapies, and surgical interventions.

However, all treatment add-ons share one common characteristic: they claim to improve the chances of having a baby (live birth rate). Evidence on whether some treatment add-ons are safe or effective is often missing or absent. These claims can attract a lot of attention with many patients opting for a treatment add-on thinking that it may be the best option for them despite there being little or no evidence to prove it is.

Treatment add-ons have varying levels of scientific evidence to support their effectiveness and safety and, at times, this evidence can be contradictory. It is important to keep in mind that for most patients, routine fertility treatment is an effective option on its own.

We aim to publish clear and reliable information about some of the treatment add-ons that lack sufficient evidence to show that they are effective and/or safe. This allows patients to make an informed decision about whether using a treatment add-on as part of their treatment is the best option for them.

To make it easier to understand the scientific evidence for each treatment add-on we have developed the HFEA’s traffic-light rated list of add-ons.


Review date: 25 August 2022

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