Introduction
PGT-A is one of the most discussed decisions in IVF. Patients often ask whether they should test their embryos before transfer, especially if they are older, have had miscarriages, or have experienced unsuccessful embryo transfers.
PGT-A stands for preimplantation genetic testing for aneuploidy. It is a test performed on a few cells biopsied from an embryo, usually at the blastocyst stage. The aim is to identify embryos with the expected number of chromosomes and avoid transferring embryos with clearly abnormal chromosome numbers.
The most important thing to understand is this: PGT-A does not increase the chance that any individual embryo will become a baby. It does not turn an abnormal embryo into a normal one, and it does not improve embryo quality.
What PGT-A may do is help with embryo selection. In some situations, it may reduce time to pregnancy by helping choose embryos more likely to implant first. It may also reduce miscarriage risk by avoiding transfer of embryos with abnormal chromosome numbers. But it is not perfect, not risk-free, and not suitable for everyone.
This article explains what PGT-A can and cannot tell you, when it may be worth considering, and how I discuss the decision with patients.
💡 Note: This blog is general educational information only and does not constitute personalised medical advice. Please consult with a fertility specialist to discuss your individual situation.
What Does PGT-A Test For?
PGT-A tests whether the embryo has the expected number of chromosomes.
A typical embryo should have 46 chromosomes, arranged in 23 pairs. An embryo with missing or extra chromosomes is called aneuploid. Aneuploid embryos are less likely to implant and more likely to miscarry.
PGT-A is designed to screen for chromosome number problems. It does not test for all possible genetic conditions. It does not detect every genetic mutation, single-gene disorder, structural problem, birth defect, or developmental condition.
This distinction is important. PGT-A is not the same as PGT-M, which is used when there is a known single-gene condition in the family. It is also not the same as prenatal testing during pregnancy.
A baby can still be born after PGT-A with other abnormalities unrelated to chromosome number. PGT-A reduces some risks, but it does not make pregnancy risk-free.
How Is PGT-A Performed?
PGT-A is usually performed on a blastocyst, an embryo that has developed to day 5 or day 6.
A small number of cells are biopsied from the trophectoderm, the part of the embryo that later contributes to the placenta. The embryo is then frozen while the biopsied cells are tested. Once results are available, a frozen embryo transfer can be planned if there is a suitable embryo.
The test result may classify an embryo as euploid, meaning the tested cells appear to have the expected chromosome number; aneuploid, meaning an abnormal chromosome number was detected; or mosaic, meaning both normal and abnormal cell lines may be present in the sample. Occasionally, PGT-A may return with no result or an inconclusive result. This can happen for technical reasons, such as sampling issues, insufficient cells collected, sample fixation problems, or DNA amplification failure. In some situations, re-biopsy may be discussed, but this is not risk-free and needs to be considered carefully in the context of embryo quality, available embryos, and the patient’s overall treatment plan.
Does PGT-A Increase Pregnancy Chances?
This is the part that is often misunderstood.
PGT-A does not increase the chance of a baby from the total group of embryos created in an IVF cycle. It cannot create more normal embryos. It can only provide additional information about the embryos already available.
If a patient has several embryos, PGT-A may help identify which embryo to transfer first. This may reduce the number of unsuccessful transfers and may shorten time to pregnancy in selected patients.
PGT-A may also reduce miscarriage risk, because many miscarriages are caused by embryos with abnormal chromosome numbers. However, miscarriage risk is not reduced to zero. A pregnancy after PGT-A can still miscarry for other reasons.
💡 Key point: PGT-A may help with embryo selection. It does not guarantee pregnancy and does not increase the underlying quality of the embryos.
Why Age Matters in PGT-A
Age is one of the main reasons patients consider PGT-A.
As women get older, a higher proportion of eggs have chromosome abnormalities. This means a higher proportion of embryos may also be chromosomally abnormal. This is why implantation rates fall and miscarriage risk rises with age.
PGT-A may be more useful when the chance of aneuploid embryos is higher, particularly in women in their late 30s and 40s, or in patients with recurrent miscarriage where embryo chromosome abnormality is suspected.
However, age alone does not make PGT-A automatically right for everyone. The number of embryos available, previous history, cost, emotional impact, and personal values all matter.
Mosaic PGT-A Results
Sometimes PGT-A results are not simply normal or abnormal. They may be reported as mosaic.
A mosaic result means the tested sample appears to contain a mixture of cells: some with the expected chromosome number and some with an abnormal chromosome number. Mosaic results can be difficult to interpret because the biopsy tests only a few cells from the trophectoderm, not every cell in the embryo.
Some mosaic embryos may not implant. Some may miscarry. Some may result in healthy babies. In some cases, mosaicism may reflect the placenta more than the foetus, or the embryo may have some capacity for self-correction. Laboratory and testing factors may also affect interpretation.
If a mosaic result occurs, counselling is very important. The decision about whether to transfer a mosaic embryo depends on the details of the result, the availability of other embryos, genetic counselling, clinic policy, and patient preference.
PGT-A Is Not 100% Accurate
PGT-A is a sophisticated test, but it is not perfect.
There can be incorrect diagnosis, including false reassurance or falsely abnormal results. This may occur because only a small number of cells are tested, the embryo may be mosaic, the sampled cells may not represent the whole embryo, or technical and laboratory factors may affect the result.
There is also a small risk that the biopsy procedure could injure the embryo. Modern biopsy techniques are generally safe in experienced laboratories, but no procedure is risk-free. In counselling, I discuss that biopsy, freezing, thawing, and related laboratory processes may potentially reduce the chance of success, and in some counselling frameworks this is discussed as up to around 15% decrease in live birth. The exact risk for an individual embryo is difficult to quantify. This is why PGT-A should not be treated as a harmless extra test that everyone should automatically do. It should be used when the likely benefit outweighs the limitations and risks.
What PGT-A Cannot Tell You
PGT-A cannot tell us everything about an embryo.
It cannot guarantee implantation. It cannot guarantee a baby. It cannot test for all genetic mutations. It cannot exclude all birth defects. It cannot replace pregnancy screening or diagnostic testing later in pregnancy.
A normal PGT-A result means the tested cells showed the expected chromosome number. It does not mean the embryo is perfect.
For this reason, patients who conceive after PGT-A should still have routine pregnancy care and should still discuss prenatal screening or diagnostic testing with their obstetric care provider.
When PGT-A May Be Worth Considering
PGT-A may be worth considering in selected situations, particularly when embryo chromosome abnormality is a major concern.
This may include women of advanced reproductive age, recurrent miscarriage, repeated embryo transfer failure, previous pregnancy or miscarriage affected by chromosome abnormality, or situations where there are multiple embryos and the patient wants additional information to help decide which embryo to transfer first.
It may also be considered when a patient wants to reduce the chance of transferring embryos that are very unlikely to implant or are more likely to miscarry.
However, PGT-A is not compulsory. Some patients prefer to avoid embryo biopsy and transfer embryos based on development and grading. That can also be reasonable, depending on the situation.
When PGT-A May Be Less Helpful
PGT-A may be less helpful when there are very few embryos available, when a patient is younger with good-prognosis embryos, or when the result is unlikely to change management.
For example, if there is only one embryo, some patients may prefer to transfer it rather than test it, accepting that the embryo may or may not be chromosomally normal. Others may still prefer testing for decision-making clarity.
The right choice depends on the patient’s age, embryo number, history, values and tolerance for uncertainty.
Practical Takeaways
PGT-A tests embryo chromosome number. It does not test for all genetic conditions or guarantee a healthy baby.
PGT-A does not increase the quality of embryos or increase the overall chance of a baby from the embryos created in a cycle.
It may reduce time to pregnancy in selected patients by helping choose which embryo to transfer first.
It may reduce miscarriage risk, but miscarriage can still occur.
PGT-A is not 100% accurate. Mosaic results, incorrect diagnosis, embryo biopsy risk, self-correction, placental mosaicism, and laboratory factors all need to be considered.
PGT-A is a decision tool, not a guarantee.
Final Thoughts
PGT-A can be a useful tool in IVF, but it should be understood clearly.
It does not guarantee pregnancy, prevent all miscarriage, or ensure a healthy baby. It does not increase the underlying quality of embryos. What it may do is help select embryos with the expected chromosome number, potentially reducing unsuccessful transfers, shortening time to pregnancy in selected patients, and lowering miscarriage risk.
The decision to use PGT-A should be individualised. It depends on your age, embryo number, miscarriage history, previous IVF outcomes, personal values, costs, and how you feel about uncertainty.
If you are considering PGT-A and want to understand whether it is appropriate for your IVF cycle, get in touch and I can help you work through the decision calmly and practically.
Disclaimer: This information is general in nature and does not replace medical advice. Please consult with your treating specialist for individualised guidance.