Pre-implantation genetic screening (PGS)

Chromosomes are genetic structures found in nearly every cell of our bodies.   

The first cell of an embryo is made up of a set of chromosomes from the sperm and another set from the egg. But if the cell doesn’t have the right number of chromosomes, known as aneuploidy, this can lead to implantation failure or miscarriage.  

Could pre-implantation genetic screening be right for me?

Pre-implantation genetic screening (PGS) is an additional screening test. 

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 PGS; 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 PGS to help us choose embryos with the right 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 PGS.

PGS lets us go deeper, allowing us to analyse the genetic makeup of embryos and check that they have the right amount of chromosomes before they’re transferred to the womb.

What does PGS involve?

Usually our embryologists choose the best embryos based on the way they look. This does work, but PGS lets us go deeper, allowing us to analyse the genetic makeup of embryos and check that they have the right amount of chromosomes before they’re transferred to the womb.

By using PGS our embryologists have up to an 85% chance of singling out embryos with abnormalities before transfer. This can improve IVF success rates for some patients and reduce both the chance of multiple pregnancies and the likelihood of miscarriage.

In PGS testing, each embryo will have one of four results.


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 counselor to discuss your options further.

No result

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 rebiopsied.

If you’d like to book a consultation please contact us

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What’s the evidence for PGS?

Some small studies have shown that PGS carried out at a later stage, the blastocyst embryo on day five or six, might be helpful in selecting a viable embryo to transfer in younger patients who are typically under 37 with no history of miscarriage or failed IVF cycles.  It is important to understand that PGS will not increase your overall chances of having a baby. 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 PGS, you should also think about the cost as it is usually very expensive.