Pre-implantation genetic testing for aneuploidy (PGT-A)
Treatment add-on with limited evidence
For most patients, having a routine cycle of proven fertility treatment is effective without using any treatment add-ons.
PGT-A for day five embryos is rated red because there is no evidence from randomised controlled trials (RCTs) to show that it is effective at improving the chances of having a baby for most fertility patients.
What does this traffic light rating mean?
Our traffic-light rated list of add-ons consists of three colours that indicate whether the evidence, in the form of high-quality RCTs, shows that a treatment add-on is effective at improving the chances of having a baby for most fertility patients.
We give a red symbol for an add-on where there is no evidence from RCTs to show that it is effective at improving your chances of having a baby for most fertility patients.
The January 2019 consensus statement (PDF) between the HFEA and ten other professional and patient bodies agreed 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.
For specific patient groups there may be reasons for the use of a treatment add-on other than improving your chances of having a baby. 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.
Our traffic light ratings only indicate the effectiveness of a treatment add-on, at improving your chances of having a baby. Specific safety concerns about a treatment add-on are included under the dedicated section ‘Is this treatment add-on safe?’
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 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, if the removal of cells is done carefully.
What’s the evidence for PGT-A?
PGT-A is traditionally offered to women over 37, patients 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.
PGT-A is now mostly carried out at the blastocyst stage on day five or six. There is no evidence from RCTs that PGT-A carried out at this stage is effective at improving your 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 having a baby. 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.
At the October 2019 Scientific and Clinical Advances Advisory Committee (SCAAC) meeting the Committee evaluated the evidence base for PGT-A. Minutes of this discussion and the evidence used to inform this discussion are available on the SCAAC webpage.
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).
- Using PGT-A may mean you have fewer embryos to use in treatment, or for freezing to use in treatment later. 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.
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.
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 this discussion and the evidence used to inform this discussion are available on the SCAAC webpage.
What are treatment add-ons?
- optional additional treatments, also referred to as ‘supplementary’, ‘adjuvants’ or ‘embryology treatments’.
- often claim to be effective at improving the chances of having a baby (live birth rate) but the evidence to support this for most fertility patients is usually missing or not very reliable.
- likely to involve an additional cost on top of the cost of a routine cycle of proven fertility treatment. Some treatment add-ons can cost hundreds or thousands of pounds each.
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, from high-quality randomised control trials (RCTs), to show that they are effective at improving your chances of having a baby.
To make it easier to understand the scientific evidence for each treatment add-on we have developed our traffic-light rated list of add-ons.
Review date: 4 January 2024