It’s Not Just Her: Male Obesity, Embryo Development, and Miscarriage Risk in IVF

In this episode of Taco Bout Fertility Tuesday, Dr. Mark Amols breaks down new research on male obesity and fertility and explains why a man’s weight may matter more in IVF than many people realize. This study looked at donor egg ICSI cycles and found that male obesity was associated with delayed early embryo development, lower inner cell mass quality, and a higher miscarriage rate, even though fertilization, blastocyst development, implantation, and clinical pregnancy rates were fairly similar across groups. 

Dr. Amols explains what this means in plain English for patients and clinicians, why a normal semen analysis does not always tell the whole story, how sperm health may affect embryo development after fertilization, and why fertility should be viewed as a couple’s issue, not just a female issue. If you want to understand the connection between male BMI, sperm quality, IVF outcomes, embryo development, and miscarriage risk, this episode breaks it down in a way that is clear, practical, and evidence-based. 

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Transcript

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Today we're talking about something that just doesn't seem right and kind of goes against everything you thought. You've probably heard obesity can affect fertility. But what you probably didn't know is that a, new study shows that obesity in men may be affecting your IVF more than most people think. I'm Dr. Mark Amols, and this is Taco about Fertility Tuesday. Let's be honest. When you hear about weight and fertility, normally people think about women, and that's because weight sometimes can be associated with a condition that can affect fertility. But guys kind of get a pass if their sperm looks good. It doesn't matter if they're overweight. We don't really think of that. But now a study has come out showing we should think about that and that our previous understanding may be wrong. So in this study, they looked, at 1,398 oocyte donation, ICSI cycles, and then they followed 7,846 embryos. And what makes this unique is they used donor eggs. So this allowed them to reduce a lot of the noise from egg quality and really focus on the male factor part of the equation. And what was shocking is that they found that the male obesity was associated with delayed early embryo development, poor inner cell mass quality, and a higher miscarriage rate, even though a lot of the standard IVF outcomes did not look dramatically different. Now, this is shocking because when there is delayed early embryo development, the women usually always gets blamed if the inner cell mass quality is not good. Again, look towards the egg quality and miscarriage rates other than translocations. When do you ever think they look at the men? This was profound. Now, it's important to understand this study was not a study saying every man with obesity is infertile. Matter of fact, by most parameters, even fertilization rates, blastulation rates, implantation rates, and even clinical prevention rates were fairly similar between the groups. But the miscarriage rates were higher when the male partner was obese, about 13.5%, compared with 9.5% in the normal weight group, which then translated into a odds ratio of 1.67, meaning there would be a significantly higher risk of miscarriage in the obese male group, 1.67 times. So that means for every miscarriage in the thin group, there'd be 1.67 in the obese group. Now, it's important to know there was a trend to a lower birth rate in that group as well, but the difference was not statistically significant. So we're going to hold off on going deep into that. Again, this is very profound because in biology, we usually think of things as binary when it comes to fertilization. Either the sperm fertilizes or doesn't fertilize the egg. Either the embryo becomes a blastocyst, or it doesn't. Or either the pregnancy test is positive or negative. Unfortunately, biology is much more annoying than that. And sometimes when things look good, there may be hidden damage under the hood. Think about this like two cars are about to run a race. One has a healthy engine, the other engine not as good. Maybe it has some more wear. Now, if you only judge these vehicles in this race by whether they started and whether they both made it out of the gate, they would look virtually the same. But once you get further down the track, one of them starts to look a little bit more like they're breaking down. And that may be what the paper is showing us, the start. Meaning fertilization may still happen, the blastocyst may still form, and the pregnancy test may even turn positive. But later on, the embryo may be less resilient, and the risk of miscarriage may be higher than we thought. Now, here's another thing that made this study kind of unique. They looked at time lapse. By looking at the morphokinetics, they were able to look at things other than just standard grading, such as the time towards development. Morphokinetics means looking at how the embryo develops over time. Not just what it looks like in a snapshot, but when it hits its key development milestones. So not just does this embryo have four cells in uniform, but. But how fast did it get there? Was it on time or was it delayed? What they found in this study was embryos from obese men showed delayed development in the early cleavage stages, especially at the 2 cell, 3 cell, 4 cell, and 5 cell stages. And as we talked about earlier, they also found that the inner cell mass was not as good. And that's a problem because that's the fetus. But here's where it gets a little crazy. The sperm looked normal. Meaning if they were blinded to the fact that men are obese, they wouldn't even know there was a difference between the men. And this is important because, it doesn't just mean, oh, obese men have terrible sperm samples. It's saying, no, they looked pretty much normal. It's only when we looked under the hood that we started to see these differences. That's because I've talked about this before. Sperm is a vector. It's just the way the sperm healing gets to the egg, but the DNA is what matters. I used to talk about how this is like the pizza delivery guy. You don't care what the pizza guy looks like. You just want the pizza to be good. That's the DNA. Now, that simplifies a little bit. But sperm also carries proteins, rna, epigenic information, and with that brings the consequences of the man's metabolic environment. So these men who are obese are probably going to have more oxidative stress. They're going to have more DNA fragmentation and chromatin abnormalities. These things are probably going to affect the embryo development and potentially even the viability of the pregnancy moving forward. And this should concern you because we usually think, well, if we're doing icsi, haven't we bypassed the sperm problem? And the point is, yes, you might have guaranteed the sperm is going to get in the egg, but you're not going to guarantee that the DNA inside the sperm is good. Unfortunately, ICSI doesn't get rid of the damaged DNA. It doesn't erase any oxidative stress that's there. It just verifies that that sperm gets through the front door. Now, does this mean you have to yell at your partner if he's overweight? Well, not exactly, but it does mean that they can't just put that trophy on the wall because they have a good sperm parameters. I've talked about this in many episodes. A, semen analysis is just looking at the morphology of the sperm and. But you're not actually putting through an obstacle course. You're not really finding out the true nature of that sperm by looking at the DNA. But it does lead to the question, how much does male factor affect things when it comes to obesity, even when the sperm looks good? And it's not unreasonable to ask your partner to lose weight, especially if you're running into issues with development of the embryos or having recurrent miscarriages. Now, keep in mind, this study doesn't prove that male obesity directly causes miscarriages in every case. This was a retrospective cohort study, which means it shows association, but doesn't actually prove causation. But the study was done well by using donor oocytes and not using men with severe male factor. They tried to even the playing field so they can look at the male factor, such as metabolism, but it's not a perfect study. But also by using donor eggs, it may have actually improved the results and that maybe with your partner's eggs it may be worse because they're not going to be as healthy as donor eggs. We know that when we use young women's eggs, they can sometimes help the sperm. We see this with men who are older. With younger women, they do better than if they were with women at the same age. And that is irrespective of just the fact that the woman's older. The younger woman's eggs actually do improve the sperm issues. So a, young woman with a man who's obese, if this truly is causing a problem, could help some of the sperm issues. So let's take a step back and talk about what does this study not prove. Well, it doesn't prove that every overweight man is going to cause a miscarriage. It also means that not every obese male is going to. Is going to cause our IVF outcome to be lower. And it also does not prove that losing weight is going to solve the problem. But what it does tell us is, is that we should stop pretending fertility is mostly a female issue with a little semen side quest attached. It's not the male health matters, and not just in the obvious ways when we're looking at the count of the sperm or the motility of sperm, but possibly in a deeper way of embryo competence. And that by the men not being healthy, could potentially lead to miscarriages and actually reduce reproductive efficiency. In the end, fertility is a couple's issue, not a solo sport. And even when the sperm looks good, male health matters. So it's not unreasonable to potentially lose weight. If the male has a high BMI and you're having issues, I can't promise you that's going to fix the problem. But I can tell you there is at least some evidence showing that it may be affecting things. But that doesn't mean we need to start blaming the men. And then we have to go extreme with diets. It may just be small changes. But the most important point is nobody gets a free pass anymore. No longer of the days of, well, his sperm is good, it must be her. Are we going to keep moving forward with. We understand biology is much more complicated than that. And what this paper suggests is that male obesity may leave its fingerprints on the embryo early on. And that may be more involved in miscarriages than we previously thought. So if you're a patient listening to this, here's the takeaway. This is not a reason to panic. This is not a reason to assume every miscarriage was because of the male obesity. This is not a reason to think fertility treatments are now hopeless because your partner is obese. But it is a reason to recognize that male preconception health matters and that improving it may be one way to improve the odds. Now, if you're a clinician listening to this, I think the bigger lesson is this. We need to expand the fertility conversation beyond fertilization rates and pregnancy tests. Sometimes the most important signal is not whether an embryo forms. Sometimes it's whether it develops on time, whether it builds a strong inner cell mass, or whether the pregnancy actually holds. This study should change the way we do things now, and that means the man is no longer just along for the ride. He's part of the biology from the very beginning. So the bottom line, this paper does not say male obesity destroys IVF outcomes across the board. It says something more subtle and maybe more important. It suggests that male obesity may quietly affect embryo development and increase miscarriage risk, even when the usual labs, such as a seam analysis, look normal. If you're interested in reading this study yourself, you can look at it in Fertility and Sterility. It was published in March of 2026, volume 125, issue number three. If you know someone who's going through fertility, maybe IVF, this may be helpful for them to know if their partner is obese. Additionally, if you're going through ivf, hopefully this helps relax you about some of the concerns you might have had with your partner's weight. As always, if you like this podcast, please tell your friends about us. 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 Belt Fertility Tuesday.