To test or not to test, that is the question

When we're so dedicated to research on euploidy, it might seem odd to be talking about whether or not to test embryos for euploidy at all.

But here’s the crux of what you need to know:

It’s ok to test, and again, sometimes there are really good reasons for doing so
It’s ok NOT to test and sometimes there’s really good reasons for doing so

So what you choose to do, ideally needs to be based on an understanding of your particular situation, your own clinic’s policies, the lab’s reporting structure, and your cycle planning in terms of euploidy add ons.

Let’s start by diving into a quick overview of what PGT-A testing is. It stands for Pre-Implantation Genetic Testing for Aneuploidy. While previously PGT-A testing was done on day 3—once culturing embryos to day 5 blasts became the norm, day 3 embryos tended to be frozen, but not tested (after multiple studies showed that biopsying at day 3 impacted transfer and live birth outcomes).

So in most cases these days, embryologists biopsy the trophectoderm (the part of the mebryo that becomes the placenta) on day 5, 6 or 7, right before they freeze the embryo. Ideally they want 100. They’ll try and take between 5-7 cells (the number of cells taken differs

PGT-A for women who can produce lots of blasts (or do so across multiple cycles), and may otherwise waste months and months transferring whole chromosome aneuploid embryos with close to a 0% chance of live birth is

I want to be clear, PGT-A is pretty damn reliable AS LONG AS, you know these things about YOUR SPECIFIC EMBRYO and YOUR SPECIFIC CLINIC AND LAB. These are the exceptions, though. In our age bracket (40+), people who have aneuploid embryos are much more likely to have simple, whole chromsome aneuploid embryos. Nevertheless, knowing and understanding the exceptions are critical.

Number of cells biopsied

The embryologist isn’t fully able to control exactly how many cells they take from the embryo. But the less cells taken, the less likely that the result is correct. If your clinic reports the number of cells biopsied, then you can take a look to determine any embryos that may not have had enough cells biopsied to have given you the most accurate result. While this may not necessarily change the result, it increases the likelihood that you may have gotten a different result (especially in cases of mosaicism).

Note I found an excellent study on this which was released in March/Apr 2024 but I cannot refind it. I’ll post it here when I do. But the accuracy of 3 cells biopsied was very low, and of 4 cells (in the vicinity of 70% likely to be inaccurate).

Lab cut offs for aneuploidy

Most to all human embryo trophectoderms are mosaic. Just like vitamin B12 levels considered high in Australia are considered normal in Europe, like most things in biology, mosaicism is a spectrum, and its definition is determined by lab cut off rates. At one end, we have euploidy, and the other, we have aneuploidy. But in fact, only 0% aneuploid cells is fully euploid and 100% aneuploid cells is aneuploid. Everything else is mosaic. So you need to know what your particular lab’s cut off rates are. And it’s important to realise that lab cut offs can change AND that it can also depend on the methodology chosen by the lab on your specific embryos

Igenomix

Type 1: 70% mosaic = Aneuploid/abnormal

Type 2: Euploid (50% or less mosaic), Aneuploid (more than 50% mosaic). Igenomix added Type 2 just in the last year after research showed that for embryos with 50% mosaicism and below, 99% of the time, when the ICM was checked, all ICM cells were euploid.

You can read more on their exact process here in their user manual

Progenesis

>40% mosaic = Aneuploid/abnormal

20-40% mosaic = Low level mosaic

<20% mosaic = euploid/normal

Cooper Genomics (Reprogenetics)

>80% mosaic = aneuploid

40-80% mosaic = high level mosaic aneuploid

20-40% mosaic = low level mosaic aneuploid

<20% mosaic = euploid

Concordance rates between trophectoderm & inner cell mass

This means, how likely it is that the part of the embryo that becomes the baby (the ICM/inner cell mass), will be the same result as the placental cells biopsied. Any tests that check for this end in a dead and unuseable embryo because you cannot actually test for this without destroying the blastocyst. However research has used research embryos to test this (even though it hasn’t been tested for thousands of embryos given the constraint of access to research embryos).

This meta analysis looked at many of these studies:

https://obgyn.onlinelibrary.wiley.com/doi/pdf/10.1002/pd.5828

The ones we should really care about are the TE/ICM studies (although this analysis included both). When not including segmental aneuploidy or mosaicism, the concordance between Trophectoderm and ICM for whole chromosome aneuploidy or mosaicism was around 95%. That’s still not nothing, that’s a 5% chance that placental cells are aneuploid while the ICM (what becomes the baby) may be euploid or mosaic.

Aneuploidies with a higher than average chance of live birth

Segmental Aneuploidy: with a reported live birth rate of around 20%-25%, segmental aneuploidy is probably the best chance at a live birth that you may have (if you have a segmental aneuploid in your already produced embryos). This is unsurprising given that the meta analysis noted at point three, when including segmental aneuploidy, found very low concordance rates between segmental aneuploidy found in the trophectoderm and the same aneuploidy found in the ICM.

https://link.springer.com/article/10.1007/s10815-024-03282-8

POLYPLOIDY EMBRYOS: This is where an embryo has a whole extra set of chromosomes (e.g. instead of two sets = 46 chromosomes, it may have a 3 or 4 or even 5 sets of chromosomes). There hasn’t been any specific studies on this, but having collected and tracked data within the PGTA Abnormal group on Facebook, we have data to suggest that PGTA has reduced predictive value when it comes to polyploid embryos. Especially XX polyploids (some data suggests XY polyploids are more likely to end in molar pregnancies).

If you want access to the data on polyploids please tag me in on that Facebook group so I know you are a member and I’m happy to share the link to the data. I cannot share it with non members as it contains member name data.

SURVIVABLE SEX CHROMOSOME ANEUPLOIDY EMBRYOS (low level life impact - XXX and XXY): Again there haven’t been specific studies on this, but we now have 2-3 examples of full anueploid XXX embryos transferred which ended in the live birth of an XX karyotype confirmed female baby. This likely means again, a reduced predictive value of PGTA as it relates to sex chromosome aneuploidies. Further, some may argue that full aneuploidy of XXX and XXY are not life threatening and in most cases, those affected are never aware they have a different karotype unless they do testing later in life. They live normal lives and studies have have suggested lower IQ or reduced fertility were based on extremely small numbers (25 people).

Chaotic embryos

The definition of this changes depending on the lab - for instance, Igenomix defines Chaotic has having 6 or more chromosomes affected as does the study that looked at this, so you would need to apply that note when assessing your own embryos against this data). This small research study found that when rebiopsied (even just from the trophectoderm), that embryos with 6+ chromosomes effected, 38% were found to be euploid. This suggests that PGTA has reduced predictive capability when it comes to chaotic embryos. And these embryos are worth transferring. This study didn’t share the age of people whose embryos were biopsied to important to note that rate of euploidy could be age-representative.

https://www.fertstert.org/article/S0015-0282(22)01577-1/fulltext#:~:text=An embryo is labeled as,as chaotic are typically discarded.

Artificial intelligence scores that indicate a higher than average chance of implantation

If you do have a standard whole chromosome aneuploid embryo (or complex aneuploid where multiple chromosomes are affected), and you also have IDA (an artificial intelligence score that is assigned to help determine the likelihood of implantation and live birth), then this may assist in at least predicting aneuploids that are more likely to implant and lead to a live birth. As an example, if you are over 42 and have an embryo with a score of 9.3-9.9, then the chance of live birth is around 15%. Now this is untested (so a portion of these would be euploid), but prioritising aneuploids for transfer is time efficient if you are considering transferring them at all).

https://www.vitrolife.com/our-products/idascore-intelligent-data-analysis-for-embryo-evaluation/

Mitochondrial activity ratio that indicates a higher than average chance of implantation (mitoscore)

higher metabolic activity and smaller mtDNA/nDNA ratio are both associated with a higher implantation potential are consistent. In fact even in this study of euploid embryos, embryos with heightened mitochondrial activity saw 0% implantation/pregnancy rate.

https://academic.oup.com/humrep/article/32/6/1282/3106141

Here in this research, Day-5 embryos with <18.19 (MsA) had an implantation rate of 81%, while those with >60, 0% implanted.

https://www.fertstert.org/article/S0015-0282(15)00373-8/fulltext

Clinic policy on embryo management between day 3 and 5

Some clinics won’t freeze a day 3 or day 7. Others won’t freeze or transfer poor quality blasts. Sometimes that’s where any C grade exists in the morphology (eg BC or CB), sometimes it includes only lowest grade CCs. The point is, if you don’t know what policies your clinic has on this, they may actually be discarding or calling an embryo done before it should be.

Clinic policy on transferring aneuploid or mosaic embryos

After all of the above, the question is, if there is an aneuploid or high mosaic per one lab’s standards and aneuploid to another standard that could be worth transferring, would your clinic actually transfer it? If not, there’s a real problem. And this is where MOST of the problem actually exists. If there were no limitations here, then we could all make the best decisions for ourselves and transfer what we wish. Most clinics these days will transfer a low level mosaic with genetic counselling, but many will advise against high level mosaic, complex mosaic and most will refuse to transfer aneuploids altogether. So if this is the case for your clinic, you either need to know your options for transporting your embryos to a clinic friendly to transferring them, or see if there is a pathway to ethics committee approval within your existing clinic.

Some other things to consider:

Determine if its worth having a day 3 transfer back up plan if things aren’t going well for freezing and PGTA so that you can at least transfer something rather than losing everything in a cycle.
If you don’t have existing data on your embryos, consider going back to the lab and requesting the original full NGS report for the embryo. Example request location for igenomics is: medicalrecord@igenomix.com. This original record can then be fed into chatGPT with a prompt for renalysis to determine exact mosaicism level rather than the lab’s original cut off points.

Perhaps it goes without saying, but the chance of a live birth for an embryo never transferred is zero. Constantly trying to push to blast for the sake of testing if your embryos are vulnerable to arrest before day 5, or if your clinic has too-strict criteria for the type of embryo they will test or even freeze may end up being counterproductive to your goal.

Test when…

You’re producing lots of blasts and time is of the essence (you’re older) or the cost of failed transfers are prohibitive
You have no baseline euploidy rate yet
You have never done a cycle but have better than average amh

Consider whether the risks of testing outweigh the benefits for you personally when (or create a back up plan that would allow you to transfer day 3 fresh) if

Your clinics policy is too harsh and they won (either they’ve discarded too harshly before or you have information from them to suggest they may)
Your clinic won’t transfer mosaics
Your clinic won’t transfer aneuploids (not all patients want to do this either so depends on whether you would)
You have already applied everything from the euploidy protocol that should benefit Euploidy and still gotten all aneuploid

https://www.sciencedirect.com/science/article/abs/pii/S1472648310617361