By Dr Sascha Edelstein
When you’re going through IVF, it’s natural to want as much information as possible about your embryos and your chances of success.
One option that often comes up is pre-implantation genetic testing (PGT). For some patients, it can be a very useful tool. For others, it may not meaningfully improve outcomes. The key is understanding what PGT can tell us, what it can’t, and when it will change decision-making.
One of the most common misconceptions in IVF is that more testing automatically means better outcomes. It doesn’t. The goal is not more information for its own sake, but the right information, used in the right context.
What is PGT?
Pre-implantation genetic testing (PGT) is an advanced screening technique used alongside IVF.
During an IVF cycle, embryos are typically grown in the lab for five to six days until they reach the blastocyst stage. At that point, a small number of cells (usually four to five) are carefully biopsied from the outer layer of the embryo, called the trophectoderm, which forms the placenta. These cells are then sent for genetic analysis in a specialised laboratory (Cooper Genomics).
At Thrive Fertility, these biopsies are performed by experienced embryologists in our on-site laboratory. While waiting for results, embryos are frozen and stored. Once results are available, a frozen embryo transfer is planned.
In simple terms, PGT gives us additional information about an embryo before transfer — but whether that information improves outcomes depends on the clinical situation.
There are a few types of PGT, but the most common is PGT-A (testing for aneuploidy, or chromosome numbers), while PGT-M tests for specific monogenic (inherited) diseases.
What do patients often misunderstand about PGT?
In practice, we often see patients assume that PGT will improve outcomes in all situations, which is not always the case.
One of the most common misunderstandings is the belief that PGT guarantees a healthy baby.
PGT only provides information about the specific genetic factors being tested. For example, in PGT-A, we assess whether an embryo has the correct number of chromosomes. A euploid result can be reassuring and is associated with a higher chance of implantation and a lower risk of miscarriage, but it does not guarantee a live birth, nor does it exclude all health conditions.
That distinction matters.
What can PGT help with?
When an egg and sperm combine, errors in chromosome number can occur. This is known as aneuploidy, and most aneuploid embryos will either fail to implant or result in early miscarriage. The likelihood of this increases with female age.
In the right circumstances, PGT-A can help identify embryos with the correct number of chromosomes. This can reduce the chance of transferring embryos that were unlikely to succeed and may lower the risk of miscarriage (evidence overview).
For some patients, it can also shorten the time to pregnancy by helping prioritise the embryo most likely to result in an ongoing pregnancy.
What can’t PGT tell us?
Chromosome number is only one part of embryo viability.
An embryo’s potential also depends on its biological function and how it develops in the lab. These factors do not always align with chromosomal status. An embryo may look developmentally strong yet be chromosomally abnormal, or appear less favourable morphologically yet be chromosomally normal.
PGT provides useful information, but it does not capture the full picture of embryo potential.
What if there is a known inherited genetic condition in the family?
In some cases, PGT is used to test for a specific inherited condition. This is called PGT-M.
If there is a known genetic condition in the family, PGT-M can help identify embryos that are not affected by that condition. However, a normal PGT-M result does not exclude unrelated genetic or health issues.
In many cases, we combine PGT-M with PGT-A, so that embryos selected for transfer are both unaffected by the specific inherited condition and chromosomally normal.
Who is most likely to benefit from PGT?
PGT is not a routine add-on for every IVF patient. It is most helpful when it changes how we prioritise embryos or manage treatment.
- Advanced maternal age: As female age increases, the proportion of aneuploid embryos rises. In this group, PGT-A can help avoid repeated transfers of embryos that are unlikely to succeed.
- Recurrent pregnancy loss: Particularly where a chromosomal cause is suspected or confirmed.
- Recurrent implantation failure: When embryos that appear favourable in the laboratory repeatedly fail to implant.
- A known genetic condition: Where PGT-M may help avoid passing on a specific inherited genetic disorder.
Are there situations where PGT may not be especially helpful?
Yes, and this is an important part of the conversation.
- Women under 35: The likelihood of producing euploid embryos is already relatively high, so the added value of PGT-A is often lower.
- Patients with very few embryos: If only one or two embryos are available, many patients choose to proceed directly to transfer. In these situations, the potential benefit of testing may be limited relative to the additional steps involved.
Is PGT something everyone doing IVF should consider?
Not necessarily. PGT is a specialised tool, not a routine step in IVF.
The decision should be individualised, based on age, fertility history, embryo numbers, family history, and personal priorities. The question is not whether PGT provides information, but whether that information will meaningfully change what we do next.
What do the results mean?
For PGT-A, results are typically reported as:
- Euploid: The embryo has the correct number of chromosomes and is suitable for transfer.
- Aneuploid: The embryo has an abnormal number of chromosomes and would not be recommended for transfer.
- Mosaic: A mix of normal and abnormal cells is present. These results are more complex and require individualised counselling.
- No result: Uncommon. These embryos are usually managed similarly to untested embryos.
How are mosaic embryos explained to patients?
A mosaic result can be difficult to interpret.
Some mosaic embryos can lead to healthy pregnancies, but outcomes vary depending on the type and proportion of abnormal cells. Because of this uncertainty, decisions around mosaic embryos are made carefully, often with input from a genetic counsellor.
What are the main downsides or limitations of PGT?
Like any medical intervention, PGT involves trade-offs:
- Not all embryos develop sufficiently to be biopsied.
- It does not guarantee pregnancy or live birth.
- It adds cost, intervention, and a delay to transfer (as embryos are frozen while awaiting results).
- Testing may show that none of the embryos are suitable for transfer. This can be confronting, but it reflects the underlying biology rather than something caused by the testing itself.
Is PGT worth the cost?
Cost is a significant consideration for many patients. When thinking about cost, it can be helpful to consider the broader picture. In some situations, PGT-A can reduce the number of transfers needed and lower the risk of miscarriage, which may reduce both the emotional and physical burden of treatment.
At Thrive Fertility, embryo biopsy and cryopreservation are performed in our on-site laboratory, with genetic analysis undertaken by Cooper Genomics, an international specialist laboratory. This allows us to integrate laboratory assessment and genetic testing within a coordinated treatment pathway.
Ultimately, PGT is best thought of as a tool to guide decision-making, not a guarantee of outcome. Used well, it can help reduce unnecessary transfers and shorten the path to pregnancy. Used without discernment, it may add cost and complexity without clear benefit.
Want to know if PGT is right for your fertility journey?
If you are considering PGT, the next step is to understand whether it is likely to change your treatment pathway. You can book a consultation to discuss your individual situation and options.