High-Level Mosaic Embryos: Rare Chances, Real Questions

What happens when an embryo never even makes it to the report? In this week’s episode of Taco About Fertility Tuesday, Dr. Mark Amols tackles the complicated world of high-level mosaic embryos—the lesser-known, often misunderstood siblings of low-level mosaics.

Learn why some labs label these embryos as “aneuploid,” why others report them as “mosaic,” and how that single label could decide whether an embryo is transferred or discarded.

We break down the true live birth odds, explain what high-level mosaicism really means, and walk through the trade-offs between not testing, testing and discarding, or testing and keeping everything.

Whether you're over 40, deep into IVF, or just weighing your PGT options, this episode will give you the clarity you need to make the right decision for your fertility journey.

🔹 Topics covered:

• What is a high-level mosaic embryo?
• Why some labs don't report them
• Statistical odds of success by age group
• Ethical and emotional trade-offs in embryo testing
• What to do with abnormal embryos if you're not ready to discard them

🎧 Tune in to find out: is a rare chance still a chance worth saving?

Thanks for tuning in to another episode of 'Taco Bout Fertility Tuesday' with Dr. Mark Amols. If you found this episode insightful, please share it with friends and family who might benefit from our discussion. Remember, your feedback is invaluable to us – leave us a review on Apple Podcasts, Spotify, or your preferred listening platform.

Stay connected with us for updates and fertility tips – follow us on Facebook. For more resources and information, visit our website at www.NewDirectionFertility.com.

Have a question or a topic you'd like us to cover? We'd love to hear from you! Reach out to us at TBFT@NewDirectionFertility.com.

Join us next Tuesday for more discussions on fertility, where we blend medical expertise with a touch of humor to make complex topics accessible and engaging. Until then, keep the conversation going and remember: understanding your fertility is a journey we're on together.

Transcript

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Today we talk about high level mosaic embryos, the ugly sister to low level mosaic embryos. I'm Dr. Mark Amols, and this is Taco about Fertility Tuesday. Last week we gave Brad Pitt a personality makeover. But this week we're asking if Cinderella's stepsister really belongs in the trash pile or if she just got a bad label. See, high level mosaic embryos are, rarely reported. Some labs call them mosaic. Others just write them off as aneuploid. Same embryo, but different fate. But what does that mean for you? Is it even worth caring about? In last week's episode, we talked about how a high level, low mosaic embryos could theoretically take your good embryo and push it to the back of the line, lowering your pregnancy chances. But in this week's episode, we're talking about embryos that might have never even got a chance. High level mosaics. And that's because there are many labs that don't even report it. At first, that could seem really bad and a very poor choice. But the question is, is it really? I think the first thing we have to define is what is a high level mosaic embryo and what does it mean? Well, a mosaic embryo means an embryo that had both normal and abnormal cells. And in the low level mosaics, it means that either 20 to 40% of those cells were abnormal. But in the high level, we're talking about 40%. And above some labs, anything over 50% is just called. Now, if you remember from last episode, this isn't like a sliding scale. There's only three to five cells taken. So for many embryos, if only one cell is abnormal, that's 33% that would fall in their low level. If two were abnormal, then it would be 66%. That would be high level. So a lot of people are worried, well, what if my embryo is 41% now it's going to be considered high level. Well, that really wouldn't happen because you would have to have multiple, multiple cells to get those type of numbers. And that would kill the embryo if you had that many cells taken. So that's really not possible. Now the question is, why would they just call it aneuploid? Well, because statistically, most of those embryos won't implant. They won't make a baby. And the desire to protect patients from the false hope is real. But here's the twist. Some of them do work. Not often, but sometimes. So if we look at the data, what we find is that when you look at high level mosaic embryos, the pregnancy chance being to a live birth is around 15, up to around the 20 percentile. Now, age plays a part in this. As people get more mature, especially around 42, we find that the pregnancy rate even goes lower. Additionally, a recent study even showed that when you looked at the embryos, such as high level mosaics, most of those embryos had what are called meiotic disorders. Those are disorders that happen during the time when the egg is developing, not later, like mitotic disorders. But this means that there was still about 40 to 45% that were labeled as high level mosaics that did not have meiotic disorders, which means they had the potential for leading to a live birth. Now, the problem is, you hear, well, wow, almost 50% came back without mitotic disorders. But then you have to go back and remember, wait a second, what's my chances of even having a mosaic embryo? And then of that mosaic embryo, what's my chances of having a high level mosaic embryo? Well, using a 2023 analysis of over 86,000 embryos out of 21,345 IV cycles, they found about 15.8% of tested blastocysts came back mosaic. And of those, they found that if you were under 35, 8.5% of those were high level mosaic, whereas when you got to age 42 and above, it was 5.5% of high level mosaics. So the point is, when you're younger, you have a higher chance of having high level mosaics, and when you're older, it's a lower chance. But what does that mean? Well, let's break it down a little further. In that same study From Armstrong in 2023, if you take that group that was under 35, you would essentially, need about 12 embryos to get one high level mosaic. And that's if obviously that company told about high level mosaics, if you were over 42, it would take 18 embryos just to get one high level mosaic embryo. Again, I'm not saying that high level mosaic embryo will lead to a pregnancy just to get one. And then the chances of having a live birth for that is only about 15%. If you go all the way up to age 44 and above, now only around 4.5% of the embryos and being high level mosaic, and now it takes at least 22 embryos to even just get one embryo to come back with a high level mosaic labeling. But the real question comes from the live birth rate. So if you take that number and say, okay, what's the chances I will get a high level mosaic, and the chance of Getting pregnant is only 15%, then that means to be able to have a live birth from a high level mosaic embryo, you would need at least 80 embryos under age 35 to get one high level mosaic embryo to come out with a live birth. If you are 42, you're in the 90s. If you're over 42, it's around 120 embryos. If you're over 44, we're talking about 150 embryos or higher to just get one live birth. Now don't get me wrong, a chance is a chance and I completely understand the idea of, well, I don't want to trade that off and not get an embryo that can potentially lead to a live birth. But when we think about how many embryos do women get over 42. Well, let's say you even get five or six. You would have to undergo 20 IVF cycles to not miss the chance of missing that high level mosaic embryo that would have got you pregnant. The point is, it's not that there isn't a chance, it's just not as high as people make it sound. So when I see patients who are afraid to use a lab because they don't report high level mosaics, it's important to understand that the actual chances of you getting a high level mosaic that would actually lead to a live birth is pretty small. So this is important. You are correct. If you are using a lab that technically does not give high level mosaic labeling and calls a mandapoid, theoretically yes, you could potentially discard an embryo called aneuploid, when in reality it's a high level mosaic. And that high mosaic could have led to a live birth. Again, under 35, it would take around 80 embryos or 42 or above. It could be anywhere from 90 to 150 embryos. And this is where the trade off really comes in. When you are younger, you do not have to do genetic testing because most of your embryos are genetically normal. But when you get older, there's a problem. After age 40, most of your embryos are abnormal. And so the question then goes, if you don't do testing, you might have to do multiple, multiple IVF cycles just to potentially have that embryo that can lead to a live birth. We're not even talking mosaic here, we're just saying a, ah, euploid normal embryo. At age 42, it takes about eight embryos to get one genetically normal. So by not doing PGT testing when you are older, you essentially don't know when to stop. You Kind of just keep spinning your wheels, hoping that, hey, you get enough embryos that eventually go into there. But there's a trade off. Now you do genetic testing. Well, then the question is, do you have them labeled embryo or not for high level mosaics? Well, let's say you get a high level mosaic. Would you stop? Well, no, you're going to keep going because you want a euploid embryo because you know the chances of that high level mosaic even leading to a pregnancy is extremely small. But you can make the argument, but if I get that and I have nothing else, I can transfer that one. And the answer is correct. And yes, the chances are it may not work, but at least you have that chance. But then on the other hand, you could say, well, there's always a chance that the embryos themselves, called aneuploid, could be wrong. Nothing's perfect. So maybe I want to transfer my abnormal, embryos. And so you could go down the path of saying, hey, I'm going to do testing, I'll call all the high level mosaics abnormal because I know the chances of one of them being an embryo that's going to lead to a live birth is low. But in the end, I'll plan on transferring all my abnormal embryos and then it won't matter because if it's in there, it will work. Now, the downside of this is there are not many clinics that will transfer high level mosaic embryos or even aneuploid embryos. Luckily for my patients, there is a clinic nearby that does do that. And so the point is, I greatly appreciate this conundrum, but I think it's important to understand you are not really taking a risk by using a clinic that uses a lab that doesn't report high level mosaics, especially if you are someone who is in their 40s or above. Because I have personally only seen one patient ever in my career that has had 90 or more embryos. And so although there is a chance, that chance is very low. And so I don't want you to feel like you're taking a trade off by using one lab over another. Sure, if they reported, that's great, but as I said, even if you get that embryo, you're going to still keep trying to get the euploid. Then eventually when you stop, you say, okay, I'm finally going to transfer that high level mosaic and I pray that it works for you. But I also don't want you to feel like you have to think you are taking a lesser path by using a lab that doesn't report it because in the end the reason they don't report it is to prevent false hope. Because when you look at the numbers it seems like, well, only seven women have to fail for one woman to have success. And that's true because a, ah, 15% live birth rate. For about every eight transfers, one will end up in a live birth with high level mosaics. But then you have to remember the number needed to get to that high level mosaic. That would be normal. And that's approximately 720 embryos. I get it. When you have infertility, any hope is hope. My goal is not to tell you you shouldn't go to a lab that has labeling for high level mosaics. I just want you to understand that it's really not making a choice of good or bad. And then if you are really concerned about this, don't discard your abnormal embryos, then you can find a clinic that allows you to transfer them and you can at least transfer those. In the end, you're not choosing right versus wrong, you're choosing which risk you are more comfortable with. Not knowing what you have or knowing but having to face the odds. Testing may not change the biology, but it can change the strategy. On how you do things. And in ivf, strategy matters. As you've heard in these discussions, too many low level mosaics and now you're picking the wrong embryo. That's the best. Having a high level mosaic. Now you may have false confidence and stop trying to get embryos when in reality the chances are more likely than not it won't work. So test if you want to clarify, freeze if you want all your options and always ask what labels am I seeing and which ones I'm not? Every person has a different path on their journey and may have different strategy. There is no right or wrong. The right answer is what's best for you. I'm going to end this podcast on why I did this podcast and it's because I was on Reddit about seven months ago. A user by the name Status Lavishness said don't use progenic labs for PGT testing. And when I read the reasoning again, it's not wrong. The person felt horrible that she did testing because in her mind she felt, wow, now I don't know if these embryos could be high level mosaic. Now mathematically she stated that she had seven embryos tested, so mathematically she wouldn't even have one high level mosaic. When you look at the odds and the chance of having a high level mosaic, that would lead to a live birth is even less than 10%. But the thing I said earlier was if there's any hope, there's hope. And that's the part that hurt, because I saw this and I realized this person felt like she made a bad decision, but in reality, she just didn't understand the statistics. We hear these stories about people having babies from abnormal embryos, and that's because the science is always changing. We're learning more and more about mosaic embryos, but on the same token, like the last podcast, I talked about how we're actually hurting our odds when we have too many high level mosaics. So it's not always black and white. What I would say is if it really worries you, don't do testing, there's no harm in that. You just don't know when to stop. And many insurances won't allow you to keep going if you have a usable embryo. So at least by testing you can keep going through IVF until you get that normal embryo. But with that choice comes a downside. If you get that mosaic embryo that's high level mosaic, do you stop? Because statistically speaking, it may not work. On the same token, if you have a lab that doesn't report it, what do you do with those abnormal embryos? Do you hope that maybe there's a high level mosaic in them? Well, statistically, we talked about what the chances of that are. Use that data to help make choices. Hopefully this episode was helpful for you. Maybe you have someone who is going through this or you're going through this. Maybe you've always wondered, did one of my embryos end up being high level mosaic? And because that clinic doesn't report high level mosaic, I threw away an embryo that would have led to a live birth. Hopefully these statistics helped you understand it a little bit better. My goal is not to demonize any clinic that's using certain labs, and it's also not to promote any clinic that's using certain labs. I just wanted you to be informed. If you find these podcasts helpful, please tell your friends about them. Give us a five star review on your favorite medium. But most of all, keep coming back. I look forward to talking to you again next week on Taco Bell Fertility Tuesday.