Pre-implantation genetic testing for aneuploidy is a genetic screening test performed on embryos produced during an IVF treatment cycle. PGT-A gives information about your embryos’ genetic health to help us select the best embryo for transfer and improve your chance of achieving a successful pregnancy.
Usually our embryologists choose the best embryos based on the way they look and develop. This certainly does work, but PGT-A lets us go deeper, allowing us to analyse the genetic makeup of embryos and check that they have the right number of chromosomes before they’re transferred to the womb.
By using PGT-A our embryologists can single out embryos with abnormalities before transfer. This improves IVF success rates for some patients and reduces both the chance of multiple pregnancies and the likelihood of miscarriage.
This means the embryo is genetically balanced with 46 chromosomes. These embryos can be transferred.
Aneuploid embryos aren’t genetically balanced and have too few, or too many, chromosomes. We won’t transfer these embryos, as they’re more likely to result in failed treatment or miscarriage.
Mosaic embryos have some cells that are euploid and some that are aneuploid. Depending on the chromosomes affected, we might still be able to transfer these embryos. If you have mosaic embryos we’ll offer you an appointment with a genetics counsellor to discuss your options further.
In less than 5% of cases, we simply won’t be able to tell whether the embryo is euploid or aneuploid. These can still be transferred or, in special circumstances, they might be re-biopsied.
If you’ve had treatment before that hasn’t worked, you’ve suffered miscarriages, or if you’re a woman in your mid–30s or older, we might recommend PGT-A; it could be that a chromosomal problem is the reason behind your failed treatments. Research suggests that more than 50% of human eggs have chromosomal problems and that this increases with age, so it’s thought to be the main reason older women can struggle to start or grow their families.
During your next cycle, we can use PGT-A to help us choose embryos with the right number of chromosomes for transfer, which could give you a better chance of success.
Patients in their first cycle who have suffered miscarriage previously or who are older than 35 may also wish to consider PGT-A.
Performing a PGT-A biopsy on embryos at Blastocyst stage has little or no effect on successful development. This is because an embryo developed to Blastocyst stage has many more cells, which can be extracted without affecting an embryo’s potential for pregnancy. The necessary freezing and thawing of embryos is highly successful with over 95% survival rate after thawing. There is therefore, a small risk that the embryo will not survive the process.
What is the evidence for PGT-A?
Large high quality research is not yet available to provide clear evidence of the success of PGT-A. It is important to understand that PGT-A will not increase your overall chances of having a baby, although it may shorten your time to pregnancy by helping us select the best embryo sooner. It may help to reduce the likelihood of having a miscarriage, but more evidence is needed to confirm these findings. When considering whether to have PGT-A, you should also think about the cost. For more information, please see the HFEA website or read our FAQs.