PGT or not to PGT – does it increase the success rate

My name is Vladimiro Silva. I used to be an embryologist. I’m originally a pharmacist. I started working in IVF in 2003, so it was 22 years this year. I’ve been the lab director at Ferticentro, a clinic in Coimbra, Portugal. I’ve also been one of the founders of Procriar, a clinic in Porto, also in Portugal.

Now we have created a group of clinics, and I’m more in a CEO role in our group. We have another clinic in Lisbon that is called Ava Clinic. We also have three clinics in Denmark, Maigaard Group, and one clinic in Greece, New Life, in Thessaloniki. It’s a group of very nice clinics. We handpick each of them, and we collaborate. It’s a really nice group of people and scientists.

What I like the most is obviously to do this: to talk to patients. I’ve been doing a lot of these webinars throughout the years, and also doing lectures in different places. As a coincidence, this afternoon I was at the university here, giving a lecture to the students’ association. It’s the most fun part of our activities when we get to share science, and especially, obviously, helping people who have a lot of questions on how to handle their treatment and their different options. Because nowadays, one of the big advantages that we have is that we have a lot of information. One of the most difficult things is how to handle all of these sometimes conflicting notions that we have in different sources.

PGT is the acronym for pre-implantation genetic testing. There are three types of pre-implantation genetic testing. First of all, how do we get embryos? We do IVF or ICSI. We fertilise eggs with sperm. Not only that, but we culture the embryos until day 5 or day 6 in the lab. Then, at that moment, we make a hole in the embryo with a laser system. We take between 5 and 10 cells, depending a bit on the embryo and how the procedure goes, and we freeze the rest of the embryo. Those 5 to 10 cells can be analysed.

The embryo, when we do this on day 5 or day 6, has more than 100 cells. The biopsy is done on a part of the embryo. The embryo at that moment is called a blastocyst, and the biopsy is done on a specific part of that embryo that is found to be very representative of the genetic content of the embryo. There were studies comparing biopsies, so cuts in different parts of the embryo, comparing the results of the analysis of those cells with the global embryo.

Sometimes embryos can have different cell lines. But as far as we know, and this is relatively well established through the last 10 to 15 years, the trophectoderm biopsy is, for sure, the most representative part of the embryo. The trophectoderm will originate the placenta, but its genetic content is closely related to the genetic content of the embryo. It’s a very effective way for us to have a notion of the true genetic content of that embryo.

There are 3 types of pre-implantation genetic testing:

PGT-M (Preimplantation Genetic Testing for Monogenic Diseases)
This is for monogenic diseases. These are diseases that are caused by just one gene. For example, Huntington’s disease, Machado-Joseph disease, there are lots and lots of rare genetic diseases. Typically, these are diseases that run in your family. For example, BRCA-associated mutations. People would know in advance that this is something. There is probably a reason why someone has been tested—neurofibromatosis, for instance. There is probably a reason. For example, if you have your parents, your brothers, your aunts, uncles—so you have cases in the family, you get tested. It turns out that you’re a carrier for some disease.

There is a chance. That chance is evaluated by a doctor, a specialist in medical genetics. He will tell you, “You have a 50% chance of having this, or a 25% chance”. It depends. There are different mechanisms of transmission. These diseases run in your family. We know exactly what we are looking for, and we will see if the embryo is a carrier for that mutation or not. We cannot tailor-make the embryos, meaning we cannot create an embryo specifically without that disease, but we can understand whether the embryo has that particular disease or not.

If the embryo is a carrier, we will not use that embryo. If the embryo is not a carrier, we will use it.

PGT-SR (Preimplantation Genetic Testing for Structural Rearrangements)
There’s a problem in the chromosome structure of the embryo. A human being has 46 chromosomes in 23 pairs. Sometimes, there are bits of a chromosome that change their place with other bits in a balanced way. So a person can be normal, without any disease or issue, because they have all the DNA they need to create the different functions of the human body.

But when they make their eggs or their sperm, we only transmit half of our DNA. We transmit 23 chromosomes that will match with someone else’s 23 to create another 46-chromosome individual. While splitting those chromosomes, since a part of the chromosome has been translocated—located next to another part of a chromosome—sometimes there are mistakes, errors in that process. In those cases, we have imbalanced transmissions, and then there could be problems.

These are situations where there is an abnormality in the karyotype. The karyotype (blood test) is a test on the chromosomal constitution of an individual.

PGT-A (Pre-implantation genetic testing for aneuploidy)

These are typically age-related. All humans produce embryos that have genetic abnormalities. The likelihood of an embryo having an abnormality increases, especially with female age. Especially above the age of 35. The older the patient, the more likely the embryo is to have genetic abnormalities.

When patients are above a certain age, in Portugal, 37 is the most common threshold, and PGT-A is often considered. Sometimes, younger patients can also do it if they have previously failed attempts. That’s another part of the conversation, and I’m sure we will get to that point. We can have a look and see if the embryos that were obtained have a normal genetic constitution. If they have a normal genetic constitution, we can transfer them into the womb. If they don’t, we can’t use those embryos.

Generally speaking, it’s pretty high at 43—high for aneuploidy, I should say. Probably 95% of the embryos are genetically abnormal at the age of 43. I have some statistics here from a study by Rubio from 2019. These show the likelihood of having an aneuploid embryo versus maternal age.

At age 43, 76% of blastocysts are aneuploid. That’s better than 95%. There’s another important point. 76% of blastocysts are aneuploid, but this depends on how you look at the statistics. We are already talking about patients who have blastocysts, which is different.

If you look at the statistics, for example, to have at least a 50% chance of one live birth at age 43, you need almost 50 eggs. If you start with a certain number of eggs, you will end up with a certain number of blastocysts. Of those blastocysts, 76% are abnormal. Depending on your reference point, this varies. If you look just at good-quality embryos, then 76% are abnormal. That’s a manipulation of the statistics because from the beginning, the chance of having a viable blastocyst at all is around 5%. It doesn’t change. It depends on what your reference point is.

I’d also like to add something because the title of this webinar is “PGT or not to PGT. Does it increase the success rate?” The answer is no.
It does not increase the success rate. PGT allows us to understand whether an embryo is viable or not. But if the embryo is not viable, PGT will not improve its quality.

In a way, it increases the success rate by preventing the transfer of embryos that are not viable. If you have 10 embryos and just 1 is viable, you save 9 negative results by transferring only the 1. In that sense, you could even say the success rate is 100% if that one embryo implants, or 0% for the other 9. Reference points are very important. PGT lowers the time to pregnancy. It helps us make decisions and evaluate options.

For example, for someone who is now 43 years old: Yes, we have lots of babies born to women at 43. We know from the beginning that only around 5% will end up having a baby. If we are lucky enough to have 2, 3, or 4 blastocysts, we know that 1 out of 4 may be viable. The problem is that not all patients end up having 4 blastocysts.

First of all, what’s a mosaic embryo? A mosaic embryo, like I said, when we do a biopsy, we culture the embryo until day 5 or day 6. The embryo has more than 100 cells. We make a hole in the embryo and we take five to ten cells from that embryo, and then we go and we analyse those 5 to 10 cells.

Sometimes, the genetic content of these five to ten cells is different. Some cells are different from the others. This is what happens with mosaic embryos: when there is more than one single cell line. It all goes down to how many cells are between the good cell line and the bad cell line, because some of these cell lines have a normal constitution, and some others have problems like a trisomy 21 or a monosomy 10.

Then the genetics lab will give us a percentage. They will tell us something like: this embryo is a 30% mosaic. There has been an evolution on what science thinks about these embryos. Initially, mosaic embryos were not transferred. Then we used to counsel patients, explaining: this embryo has a 20% or 30% or whatever cell line, and we would discuss with the patients the type of attitude to have.

More recently, in 2022, there was a study, which we call a landmark study, that showed that mosaic embryos have an equivalent developmental potential when compared to fully euploid embryos. These were embryos that had 50% or less mosaicism. The conclusion is that 50% or below have the same probability of implantation as an embryo classified as fully euploid. Why does this happen? Because the normal cell line typically takes over the embryo. They overlap with the development of abnormal cell lines.

Human embryos, when they have normal characteristics, can exclude from the embryo the abnormal cell lines. Mosaicism turns out to be a relatively normal feature of human embryos. A lot of us are born from mosaic embryos and we don’t know that.

Typically, what the genetics labs are reporting is: if the number of abnormal cells exceeds 50%, they classify that embryo as unsuitable for transfer. If mosaicism is 50% or below, they classify it as suitable to transfer. The study I mentioned showed that 50% or below mosaic embryos have the same probability of implantation as fully euploid embryos.

And, because we are using 10 cells or 5 cells, not the 100 cells of the embryo, since using all the cells would destroy the embryo, then even the embryos we classify as fully euploid might also be mosaics. We just weren’t lucky enough to pick up the mosaic cell or the other cell line.

So it’s something that is part of normal human evolution. As of now, we know there is a threshold for mosaicism. Currently, it’s at 50%. Maybe in 6 months it will change. Maybe tomorrow it will change. There are a lot of research institutes worldwide doing this type of test all the time. For the moment, this is where human knowledge is.

Yes, that’s a very good comparison. You wouldn’t throw away that apple. You would still eat it. And by the same token, it’s important to understand that with these embryos.

Just from the people I’ve spoken to, let’s say someone gets results like this:

• One embryo is euploid.

• One is a low-level mosaic (20–50%).

• One is a high-level mosaic (50–80%).

• One has an inconclusive result.

Normally, we need to look not just at calling an embryo mosaic, but also at what type of mosaicism it involves. Among genetic abnormalities, there are some that are compatible with life and others that are not.

What we sometimes do is:

• 50% or less, we transfer—equal chances.

• No distinction is made between embryos considered fully euploid.

Higher degrees of mosaicism: those are not top-priority embryos. We save those embryos for last. Among those, we look into the type of genetic abnormalities. This is something discussed with the patient and our genetic specialist. I’ll give you an example.
There was a patient who had 10 blastocysts. That was good. But the 10 blastocysts were all abnormal, each had a genetic abnormality. This patient still wanted to transfer. There is a way to rank these embryos. She asked to start with a trisomy 21. But in our advice, this was the last embryo to transfer. Why? Because it’s viable. We have babies with Down syndrome all the time, and this is compatible with life.

This patient was saying, “What if there is mosaicism inside?” We typically prefer to transfer embryos that involve genetic abnormalities that are not compatible with life. Why? Because either those cell lines will die, like a trisomy 4, which is incompatible with life, or the normal cell line takes over.

So, either the embryo will not implant, or the abnormal cells will not lead to a baby. Obviously, the lower the percentage of mosaicism, the better. Sometimes, when we don’t have anything else, we give proper counselling to the patient. We tell them: the difficult decisions are the ones involving cell lines that are compatible with implantation. This is a long discussion. We inform the patients and discuss with them in detail what can happen if the bad cell line takes over, especially if it is a high-risk mosaic. Some patients prefer to transfer them. Some don’t. This is decided on a case-by-case basis.

Normally, when we have a Trisomy 21 case, it’s a formal indication to do PGT-A in a subsequent cycle. This person has a formal indication to do PGT-A, no question about it.

Actually, in Portugal, our regulator sets a series of rules for situations where patients are allowed to do PGT-A regardless of their age, and this is one of the cases, when we have an affected pregnancy. There is a formal indication for that. The risk is especially age-related, but we know that having an affected pregnancy slightly increases the risk of having a second affected pregnancy. However, if you do PGT-A, we will know beforehand.

Nowadays, when we do PGT-A, we still advise patients to do prenatal testing, but in my career, I’ve never seen a case where an embryo that was found to be viable after a PGT-A led to an abnormal embryo during the pregnancy. It’s more of a theoretical possibility, and because of that, we advise patients to do amniocentesis and so on. But like I said, I’ve never seen it myself.

I actually wrote down some numbers from an article that is quite illustrative of what we are discussing here. This is a study published in 2021. A group studied 2,600 embryos. They did PGT-A on all 2,600 embryos, and then transferred these embryos into the womb without the doctors knowing the results. It was a double-blinded study. They compared the embryos classified as euploid with the results obtained from embryos classified as aneuploid.

The euploid group—the viable embryos—had an 82% pregnancy rate, while the aneuploid group had a 40% pregnancy rate. A big difference. However, in terms of live birth, the euploid group had a 65% live birth rate, while the aneuploid group had 0% live births. Zero. So they all miscarried.

This is how effective PGT-A is. From the embryos classified as euploid, they had zero cases of embryos identified as abnormal during the pregnancy, for example, in an amniocentesis. This shows PGT-A was able to identify which embryos were viable. 65% of those cases led to a live birth, which is what people want. They want a baby at home, not just a positive pregnancy test. The embryos that were not normal, which would have been identified by PGT-A, were still transferred because it was a double-blinded study. None of them resulted in a live birth.

Obviously, some things cannot possible to be identified through PGT-A. Just because an embryo is euploid doesn’t guarantee it will be 100% healthy. I remember a case where an euploid embryo was transferred, everything was going great until the 12-week scan. Something was looking odd, and then at the 16-week scan, something was definitely wrong, and she miscarried. It’s very rare, but it is important to note that PGT-A is a powerful tool, but it’s not a guarantee.

We need to split the answer into two parts. When we are talking about possible genetic diseases, we’re not just discussing what can be identified by PGT-A. PGT-A is for chromosomal abnormalities. There are lots of other diseases, monogenic diseases, most of them recessive, that can be excluded from the donor egg from the beginning. This is a common mistake or a common point of confusion for patients.

For example, a lot of our patients do what we call carrier screening tests. This means that if you come to one of our clinics, let’s say, doing an egg donation cycle, there’s the male element of the couple and an egg donor. We can screen the husband for 2,200 diseases. We can do the same test on the donor and see if they are carriers for the same recessive diseases.

All human beings are carriers for something. Donors are human. So, donors are carrying something. Patients carry something. The risk exists when they carry the same recessive diseases. If that happens, and that happens in 2 to 5% of cases, there is a 25% chance of having a genetic abnormality. So 25% out of 5% is 1.25%. That’s the chance. Again, it depends on your reference points.

We’ve had lots of cases of unfavourable matching results where we were selecting a donor based on the patient’s characteristics, donor profile, all the details, and then, doing the matching with the donor, we saw that the male partner and the egg donor were carriers for the same mutation. The same with the female patient and the sperm donor. It also happens, or sometimes in a double donation, that both donors can be carriers.

Another completely different thing is the likelihood of having a chromosomal abnormality in an embryo obtained from egg donation. Then we enter the philosophical question and the debate going on in the scientific community.

The study I quoted is clear. In that study, with 2,600 embryos, they found absolutely no embryo identified as not viable that implanted. When we talk about 98–99% in 2,600 embryos, there could be some exceptions. But in this series, there were none. The results are very clear. There’s no question, it puts it in your favour.

If you go theoretically, it’s like when we watch movies, saying that the paternity test shows someone is 99.99% likely to be the father. 99.99% is one out of 10,000. Portugal has 10 million inhabitants, so that would mean 1,000 people with that probability.

But at the end of the day, it’s a theoretical risk. It’s the limit of science, the tests we can do in the lab, the methods that exist, the capacity of the equipment we use. We need to understand and accept that.

In medicine, there are two numbers we don’t like: 100% and 0%. We need to understand the boundaries of what we are saying. But here, I would say it’s a very effective method. It’s pretty clear.

The likelihood of an egg donor having a chromosomally abnormal embryo (aneuploid embryo) is around 37%. Under 35 is 40.5%. Egg donors are 37%. In Portugal, the threshold is at 49.7. Which means that above a 50% chance of having an abnormal embryo, we can already do PGT-A. However, the risk exists below that.  In my opinion, and this is what I was saying in the beginning, I don’t think 37% is an acceptable risk, so I think PGT-A should be done. However, in Portugal, for instance, it’s not legal. We can only do it above the age of 40.

The data from Igenomix, one of the biggest genetic labs in the world, is their internal data. We can see that below the age of 35, the implantation rate with PGT is 60%. And here we can see that the percentage of aneuploidy is 37%. What they claim is that you get more or less the same probability of pregnancy whether you use donor eggs or PGT-tested embryos. It’s arguable. I don’t want our patients using an egg donor, because it’s a very difficult decision. For example, someone getting to the conclusion that they need too many embryos, we saw the theoretical exercise at the age of 43; we can do the same at the age of 45. It’s not impossible. It’s worth trying. There’s a moment for most patients when it will not work with their own eggs. The solution is either to try again or to move on with egg donation. It’s a very difficult decision. Even from a psychological standpoint, they need to pass that point.

Having a trisomy 21 pregnancy after all of what they’ve been through can be devastating. This is why I think it should be allowed. Unfortunately, I’m not the regulator. I’m not in charge. There are scientific societies with recommendations that go exactly in the opposite direction. It’s an ongoing debate in the scientific community. I’m siding with those in favour of doing PGT for all cases.

If you go and look at 10,000 cases, you can see statistically speaking it’s 60% with PGT and 60% with donor eggs. Why do PGT?  That is your life, which is zero or 100%. There’s no middle ground. One thing is looking at the population. Another thing is looking at a patient’s individual case. I would be in favour of doing it. Unfortunately, we have to comply.

Going a little back, AMH 1.85. I’m assuming it’s nanograms per millilitre. We need to be careful with that. If she had 10 eggs, I’m sure it’s nanograms per millilitre. One or two good blastocysts out of 10 eggs is a good result at the age of 42. Typically, we would expect 30–40%, so it’s a little below, but she’s 42. We can’t ignore the age factor.

I would use PGT-A, also with 5 failed rounds of IVF already. This patient is exactly a poster case in favour of PGT-A. She failed 5 times, probably because the clinic told her, “You have good blastocysts here. They gave her a lot of hope, and then she got disappointed with a negative result, and she doesn’t know why. Was it her womb rejecting the embryo? Maybe an immune condition? I bet she has done lots of tests—endometrial biopsies, hysteroscopies, complex immune testing, and so on. We don’t know the main reason, which is whether the embryos were viable or not. Even if it was just 1 blastocyst, I would for sure test it. It helps her to decide. It’s completely different to have 5 failed attempts and then do it a 6th time and get aneuploid embryos again—maybe it’s time to think about egg donation.

On the other hand, if she’s having viable embryos, and the embryo is genetically normal and still no pregnancy, then we must think about something else: the endometrium, the immune system, infections, microbiota.

There are lots of things to look at to optimise before going through. PGT-A is an excellent decision tool for cases like this. It helps the medical team direct the investigations to understand why treatment is not working, and to control all the factors we can. Unfortunately, in medicine—in reproductive medicine—we can’t control all the factors, but the more we can control, the better.

Typically, most labs define chaotic embryos as embryos that have 6 or more genetic abnormalities. I’ve also seen cases where embryos with 4 simultaneous abnormalities were already classified as chaotic. To be honest, I don’t think so. The study I was referring to earlier had zero of these cases.

There are studies published where aneuploid embryos were transferred, and normal kids were born. However, some of these were exceptions, done many years ago, and with different genetic labs. Nowadays, with the quality of most genetic labs, the quality of the clinics doing the biopsies, and with current methods of next-generation sequencing, it’s very unlikely.

There is a theoretical chance, because detection rates are 98–99%, but patients have to understand we are talking about very, very low chances. We don’t say zero in medicine, but it’s certainly very close to zero.

Normally, I tell patients this: PGT-A is sometimes very blunt. It tells us the truth about the embryo. And a lot of times, we don’t want to hear that truth. The role of the clinic is to give patients the cold and emotional information. Of course, we need to be compassionate and understand the situation, and I believe we do that. We try to understand what that person is going through.

But it’s also important to provide very objective, solid scientific information. The way you feel about that information is one thing. But that information is the baseline where your decisions and emotions must be based. Unfortunately, sometimes we don’t have good news. We can’t sugarcoat it. We need to tell the patient exactly what the situation is. We can look to the future, see the perspectives, alternatives—whether it makes sense to try again or move to donor eggs.

There are pros and cons. We discuss every detail. But PGT-A has this cold side, it tells you information that, unfortunately, is not what we want to hear most of the time.

I don’t have any experience with this. I’ve seen some studies; those are very initial studies with very low numbers of patients. In medicine, we need to be very careful. We can’t block science from happening—IVF started with a single case in 1978, and now we have 8 million babies, so it’s a success story.

I’ve been 22 years in this field and I’ve seen a lot of things come to market with great promises and a lot of hype. It’s that Gartner curve, you know, initially everyone thinks that we’re finally having a solution for this and that. Unfortunately, I would say most of these new therapies end up not showing as promising as they were in the beginning.

It’s our biggest fear, obviously. When I started working in this field, we were doing day three biopsies with embryos that had eight cells, and sometimes we were taking two out of eight. Different times. They were analysed by FISH. FISH is a technique that is used to look at 5 chromosomes. A lot has been going on initially. Then we moved into inner cell mass biopsies and then trophectoderm. There were paper after paper being published comparing the different types. So, from the day three embryos, inner cell mass, and trophectoderm, the trophectoderm seems to be the more reliable one.

I’m also from the time when we were picking a little bit from the inner cell mass and a little bit from the trophoectoderm. Then we moved to—and when I say we, I’m talking in the name of all IVF centres, the main ones. Nowadays, I don’t think there’s anyone doing anything but trophectoderm biopsies. We need to trust the science that comes before us. Going back to that study, 65% of the embryos that were considered normal ended up being born. 0% of the ones that were considered not normal ended up being born, even though there was a 40% implantation rate.

If in that study the inner cell mass was okay, but the problem was only on the trophoectoderm, there would be at least one baby on the other branch of the study. So it is not impossible, I would say it’s unlikely in light of what we know and what science is telling us recently.

Yes. So first of all, and also I’m very mindful of the people who were asking a lot of interesting questions here. Please feel free to send me an email. I’m very happy to answer all of you directly. We can even chat, do a Teams call, whatever. I’m really available to talk to each one of you. Unfortunately, we need to be mindful of the time.

Going a little back on this PGT, whether to do it or not question, normally I see this as a fraction. When we look into the pregnancy rates with or without PGT, on top of the fraction, we have the babies born. Those will always be the same. If we have, let’s say, 10 embryos, 2 of them are viable, and 8 are not viable. On top of the equation, we will always have the 2 that are viable.

In this scenario A, where we don’t test the embryos, we have 2 out of 10 attempts. So we transfer 10 embryos, and we get 2 pregnancies, 20%. If we do PGT and we are able to identify these two, we will only transfer these two, and then it will be two over two, which is 100%. At the end of the day, that’s how I believe the calculations should be made.

Because obviously, if we transfer all the embryos that we have from a given cohort, we will see at the end if there was an implantation or not. However, that will not give us information on the side. For example, in cases where the problem is with the endometrium, there are a lot of factors that we will not be addressing because we don’t know why the treatment is failing.

For example, if we are unlucky enough to, in this particular example, where we have two viable and eight that are not viable, if we are unlucky enough to start with the bad eight, this patient would have 8 negative embryo transfers. She will be devastated emotionally, financially, and physically. She will have done multiple endometrial biopsies, hysteroscopies, whatever exams you name it. And at the end of the day, she still has to—maybe she gives up and wastes the two viable embryos.

I think PGT is a very useful tool to help us make decisions. But we need to be very mindful of what it is or what it isn’t. It isn’t a way to improve the overall results. It will not make your embryos better. It will allow us to think, to make decisions, and to lower the number of failed attempts. That’s a very important one. Also to optimise what we can do regarding the endometrium and the uterine environment, and other factors.

The take-home message here is that you need to understand where you are. See what else you can do to improve your chances. Or, if you don’t have viable embryos, then everything is pointless. It’s preferable either to try again, depending on the analysis that we do—the assessment that we do—or to move with embryo donation, egg donation. I mean, there are different possibilities. Or just stop the attempts. It’s also a very acceptable decision. So it’s a tool to make decisions, to think, to consider—not a miracle, but a very important piece of information in the context of your treatment.