Beyond Chromosomes: What PGT-A Results Actually Tell You — And What They Don't

Why PGT-A Has Become One of the Most Talked-About Tools in IVF

If you've been through an IVF consultation recently, there's a good chance PGT-A — preimplantation genetic testing for aneuploidies — came up in the conversation. And if you've done any research online, you've likely encountered two very different opinions: some sources describing it as a near-essential step in modern IVF, and others questioning whether it's always necessary at all.

The truth, as is often the case in medicine, sits somewhere in the middle — and it's more interesting than either extreme suggests. PGT-A is a genuinely powerful tool when used in the right context. But it's also one of the most misunderstood tests in fertility medicine, and patients who go in without a clear picture of what the results mean — and what they cannot tell you — often find themselves confused, distressed, or making decisions based on incomplete information.

This post is here to change that.

What PGT-A Is Actually Testing

Every human embryo should contain 46 chromosomes — 23 pairs. When an embryo has the wrong number of chromosomes, it's called aneuploid. Most aneuploid embryos either fail to implant at all, result in early miscarriage, or — in a smaller number of cases — lead to a pregnancy affected by a chromosomal condition such as Down syndrome (trisomy 21).

PGT-A works by removing a small number of cells from a day-5 or day-6 blastocyst embryo (from the outer layer, called the trophectoderm, which becomes the placenta — not the inner cell mass that becomes the baby). Those cells are sent to a genetics laboratory, where the entire chromosomal complement is analysed. The embryo is then categorised as:

• Euploid — chromosomally normal, and considered suitable for transfer
• Aneuploid — chromosomally abnormal, and typically not transferred
• Mosaic — containing a mixture of normal and abnormal cells, which requires a more nuanced conversation with your doctor

The appeal is clear: if you can identify which embryos are chromosomally normal before transfer, you can potentially reduce the risk of failed cycles and miscarriage, and improve the efficiency of your IVF journey. In theory, you transfer fewer embryos, experience fewer losses, and reach a successful pregnancy faster.

Where the Results Get More Complicated

Here's what many patients aren't told upfront: PGT-A results are probabilistic, not absolute.

The biopsy samples a small number of cells from the trophectoderm — typically five to ten cells out of the hundreds or thousands that make up a blastocyst. There is a recognised rate of what scientists call false positives: embryos that test as aneuploid but are, in reality, chromosomally normal throughout most or all of their cells. This occurs partly because of a natural phenomenon called confined placental mosaicism, where chromosomal abnormalities are present in placental cells but not in the embryo itself.

Studies have documented cases of healthy babies born from embryos that were classified as aneuploid by PGT-A — embryos that would have been discarded under a strict interpretation of the results. This doesn't mean the test is flawed or shouldn't be used. It means the results should always be interpreted carefully, in conversation with an experienced clinician, rather than treated as binary verdicts.

Mosaic embryos sit in a particularly nuanced space. Once considered untransferable, there is now growing evidence that certain mosaic embryos — particularly those with lower levels of mosaicism or involving specific chromosomes — can result in healthy pregnancies. At Iswarya Fertility, our team discusses mosaic embryo cases individually, taking into account the specific chromosomes involved, the level of mosaicism, the patient's overall embryo cohort, and their clinical history before making any recommendation.

Who Benefits Most From PGT-A — And Who May Not Need It

PGT-A is not a one-size-fits-all recommendation. The patients who tend to benefit most include:

• Women over 37, where the natural rate of chromosomal errors in eggs rises significantly with age
• Couples with a history of recurrent miscarriage, where chromosomal abnormalities in embryos are a likely contributing factor
• Patients who have experienced multiple failed IVF transfers with good-quality embryos, where aneuploidy may be an undetected reason for implantation failure
• Those who produce a large number of blastocysts and want to prioritise which to transfer first

On the other hand, PGT-A may add less value — and sometimes unnecessary complexity — for younger patients with no history of loss or failed cycles who produce only one or two blastocysts. Testing a small number of embryos also carries a statistical risk: you may end up with no euploid embryos to transfer, when at least some of those embryos might have implanted successfully without testing.

This is why the decision to pursue PGT-A should always be personalised. Your age, your diagnosis, your embryo numbers, your history, and your personal priorities all matter.

Understanding a Euploid Embryo Transfer — Managing Expectations

One of the most important things to understand is this: a euploid result does not guarantee a successful pregnancy.

Chromosomal normality is one of the most significant factors in embryo viability — but it is not the only one. Implantation also depends on endometrial receptivity, the quality of the uterine environment, immune factors, and elements of embryo quality that current genetic testing cannot yet assess. Success rates for single euploid embryo transfers are meaningfully higher than for untested embryos, typically ranging from around 50 to 70 percent depending on the clinic and patient factors — but that also means a proportion of euploid transfers do not result in a live birth.

Understanding this distinction matters enormously for emotional preparation. A euploid embryo gives you the best possible start — it does not eliminate all uncertainty.

Making the Decision That's Right for You

At Iswarya Fertility, PGT-A is never recommended as a default add-on. Our consultants take time to explain the evidence behind the test, who is most likely to benefit, what the results will and won't tell you, and how to interpret outcomes — including mosaic results — in a way that actually informs your next step rather than simply adding to your anxiety.

If you've been offered PGT-A and want to understand whether it makes sense for your specific situation, or if you've received PGT-A results that you're finding difficult to interpret, we encourage you to come in for a detailed consultation. The best fertility decisions are always made with the full picture — and that's exactly what we're here to help you build.

Book a consultation with the team at Iswarya Fertility and let's talk through your embryo testing options with the clarity and honesty you deserve.

Frequently Asked Questions

Is PGT-A testing compulsory for IVF?

No, PGT-A is optional and not necessary for every patient. It tends to offer the greatest benefit to women over 37, those with recurrent miscarriage, or those with a history of repeated failed transfers. Your doctor should help you weigh whether it's appropriate for your specific situation.

What happens if all my embryos come back aneuploid?

This can be a very distressing result, but it doesn't necessarily mean you cannot have a biological child. Depending on your age and circumstances, your doctor may discuss further stimulation cycles, the possibility of reviewing mosaic embryos, or exploring other pathways. It's important to have this conversation in detail rather than drawing conclusions from a single cycle.

Can a mosaic embryo lead to a healthy pregnancy?

Yes, in some cases. Research shows that certain mosaic embryos — particularly those with lower mosaicism levels or involving specific chromosomes — can result in healthy live births. Mosaic embryo transfers are handled on a case-by-case basis, and close monitoring during pregnancy is typically recommended.

Does a euploid embryo guarantee a successful transfer?

Not guaranteed, but it significantly improves the odds. A chromosomally normal embryo still needs a receptive uterine environment to implant successfully. Success rates for euploid single embryo transfers are generally higher than for untested embryos, but a proportion of transfers will still not result in a live birth.

Does PGT-A testing damage the embryo?

The biopsy procedure is performed by highly trained embryologists and is considered safe when done at an experienced centre. Cells are taken from the trophectoderm — the outer layer that becomes the placenta — rather than from the inner cell mass that develops into the baby, which minimises risk to the embryo.