Pooling Frozen Sperm for IUI—and What Freezing Really Means

Freezing is one of the most powerful tools in modern fertility—but it’s also one of the most misunderstood. In this episode of Taco Bout Fertility Tuesday, Dr. Mark Amols unpacks the science behind freezing sperm, eggs, and embryos. Why do eggs and embryos need vitrification while sperm are slow-frozen? Does freezing harm fertility? Why can’t multiple sperm samples just be frozen and combined for IUI? And does the length of time embryos are frozen affect success?

From the history of freezing to survival rates and real-life applications, this episode answers your biggest questions and clears up the myths.

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.

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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

0:01

Today we're talking about chilling out, literally. And talk about what freezing really means. Inf ferility treatments. I'm, Dr. Mark Amols and this is Taco about Fertility Tuesday. Now, I get asked about freezing all the time. Patients hear about freezing eggs, freezing embryos, freezing sperm, but what does it actually mean? And does it hurt them? Well, one of the listeners asked a brilliant question. If my sperm count is low, why cant I just freeze 10 sperm samples, mix them together and then use that for iui? Wouldn't that be easier than ivf and possibly even lower cost? And that's the kind of question I love because it seems so logical. But once you understand the biology, the dancer gets a little bit more interesting. So let's dig in a little bit more. So here's a fun fact. Freezing hasn't always been this good. Matter fact, back when I was a resident, we usedually use slow freezing. Even when I became a fellow, slow freezing was still used. It wasnt until a little bit later that vitrification not only was used, but really became the preferred method of freezing. But the question is why? Well think of slow freezing like putting a soda in your freezer. What happens? Well, you come back, an entire freezer is frozen. Was sod all over the place. And that's because when the water is freezing, it expands. This is the same reason why ice floats on your glass of water. And the problem is when you freeze eggs or embryos using a slow freezing method, you start to develop these ice crystals from the expansion and that starts to tear things apart. Just like the sodaam but with vitrification. Instead of slowly freezing everything, we freeze so fast that crystals cant even have time to form. Basically, everything turns into a glass like state. Perfectly preserved. In some ways, you shouldnt even think of them as being frozen. You should almost think of everything as just moving very, very slow. Vitrification means glass like. And so when you look at glass, we think of it as a solid, but technically its structure is actually like a liquid. And so if you wait millions of years, glass will start to drip. And so what is great about vitrification is not only are we able to preserve these embryos and these eggs, but we dont create the crystals. And theyre technically not frozen in the way we think of it. Theyre just moving very, very slow. Another example would be with food. If you take strawberries and put them in your freezer, they come out mushy. Yet when you flash freee sushi, GRY tuna, it stays fresh. The flash freeze is preventing the ice crystals from forming. And that's the important part. And really vitrification is what allowed us to eventually be able to freeze blastocyst. Back in the day when we were doing slow freezing, a lot of people used to freeze the embryos at either the 2pm stage or even at the morula stage, because this is a point where there was more compaction and less fluid. When you finally got to the blastocyst, there was a ton of fluid inside of the embryo. And so slow freezing didn't work as well. Vitrification came around and now all of a sudden we could start freezing day five embryos. Now there's more that comes to that story, such as better culturing that allowed us to get the day five. But the point is vitrification changed a lot of things. So when we say freezing, were not talking about sticking your embryos next to your frozen pizza rolls. Were talking about liquid nitrogen at minus 196 degrees Celsius. Now that may sound cold, but remember thats in Celsius. In Fahrenheit, thats 384.8 degrees negative. Basically, at, that temperature, biology is paused, time is paused. The cells at that point don't age, they don't degrade, they just wait until they're ready to be used again when we thaw them. So here's the interesting thing. You would think that we're freezing everything the same, but we're not. The way we freeze sperm and the way we freeze eggs and embryos are different. And this comes back to that point of water. Eggs and embryos are giant water balloons. If you slow freeze them, crystals form and destroy them from the inside. This is why we need vitrification. The fast freezing stops the crystals from forming. Now, sperm have very little water inside, but their weak spot is in the fragile membrane around them. So when we freeze them slowly with protect the buffers such as glycerol, sucrose or even egg yolk, the lipids in egg yolk will act like bubble wrap around the sperm, protecting the fragile membranes. And yes, it is actual egg yolk, the same thing you have at breakfast. So when we freeze sperm, you usually use slow freeze. And when you freeze eggs and embryos, you use vitrification. Now sperm can be frozen through vitrification, but the quantity has to be much smaller because it has to fit on a special straw. These straws are specifically made to be able to freeze things like eggs and embryos. But when it comes to sperm, you can only put the amount of sperm you can fit into a tiny droplet. And that works great if you're going to freeze some eggs or embryos because they can all fit into one tiny droplet. When we were talking about sperm, it takes millions for things like IUIs or freezing for the future. So yes, if you only want a small amount of sperm, you could use vitrification. But because, that isn't really practical, the gold standard for freezing sperm is going to be slow freezing, whereas the gold standard for freezing, ACHG and embryos is going to be vetrification. So overall, the reason we don'vitrify sperm is because one, you cannot freeze a lot of it, and two, unlike eggs and embryos that use super strong cryotectants, sperm don't work as well with that. And so when you vitrify it, it goes under more stress, it gets damaged. So the survival and DNA integrity aren't always better with vitrification, it's better with slow freezing. So then we get back to the question of, survival rates, and here's where patients really should be listing and where your ears may perk up. What is the chances of survival? Well, if we're talking about eggs, survival with vitrification is usually greater than 90%. And with embryos it's even higher, probably greater than 95% in a good lab. But what about sperm? Now, it's not vitrification, so we're talking about the slow freezing, but it's somewhere about 50 to 70%. That seems really strange because you always hear this saying that sperm freezes really well. And that's true, but not when it comes to the percentage that survives. So how can we make this type of claim? Well, because we don't need that much sperm. So even we freeze 1000, we still get 500 and we're freezing millions. And so as long as we get so many sperm, the fertilized eggs and those egg numbers are going to be in reasonable numbers. It's nothing to worry about. Another interesting fact about freezing is when you freeze eggs, when you freeze an egg, you have to use ICSI in the future. And similar to the last episode in this podcast, I talked about how the zona pelousa, which is the shell, hardens, preventing the sperm to naturally get through the fertilized egg. So although it doesn't hurt the egg, it does change the egg a little bit, make it not being able to be fertilized naturally. So this gets us back to the listener'question why not pull a bunch of frozen sperm to do an IUI versus suspndending on an expensive IVF cycle when you can just freeze a bunch of samples and then thaw them. Well, here's where the issue lies. Let's say you need around 20 million sperm to be able to do an IUI and you only have 4 million sperm. Well then you say, okay, well then all I need to do is free five samples. But the problem with that is that's assuming all five samples would thought perfectly to get 20 million sperm again. But in reality you're going to lose 50 to 70% of that sperm, which means you're going to need to freeze between 10 to 12 samples just to be able do an IUI. All of sudden, the cost effectiveness is not there. And let's not even talk about theount time you have to put into that. That's like a full time job because remember, you can only freeze every two days. So to do one iui, you would have to basically freeze for a month to do one iui. So the question is a brilliant question. Matter of fact, when I was in residency and I had fertility problems, I asked the same question and unfortunately they didn't give me a very good answer. They just said you can whereas I giving you the real answer it not that you cant, it just not effective. You would have to freeze so many samples. That'not worth it. But what if you'just really close? Let's say you do make 12, 14 million sperm and let's say that when they go to do the ii, it's just a little bit less than what you need. Well, that's a perfect example of where you can do this. Now you only need to freeze maybe an extra sample or maybe three samples. And that way on the day of if you have a bad day and your count'a little bit low, you thaw, one of those samples and added to it. And that's a perfect situation where that can work. However, if you're the type of person where you absolutely need ivf, it's probably not going to be effective to freeze a bunch of samples to try to now do IUIs. So a couple more interesting points. One of the questions that I get asked is, does it matter how long it stored? Are my embryos getting bad the longer they'stored? And the simple answer is no. Once they are frozen, they are paused in time. There have been embryos stored for 20, even 30 years that have led to healthy babies. So we know it'safe and we know it doesnt really affect the embryos that much. They dont really Go bad. Whereas I would say get freezer burn. Now, there was a retrorospective study that showed embryos frozen for a longer time. Meaning, like, lets say if you do a transfer right away versus six months, there was slightly lower success rate. But heres the key, Takeay it doesnt mean the Ambross got worse. It probably means that the patients who waited had tougher fertility problems and needed time to fix those problems, like polypctomies, endometriosis and other stuff. So there was an association, but not causation. So if you'not ready to transfer that time, take your time, there is no harm in waiting. The other situation that comes up with a long time being frozen are embryos that are your last embryos. So if, let's say you have six embryos and for the first six years you're using three of the embryos and you get pregnant, obviously those embryos years later are not going to be of the same quality. Not because they get hurt in the freezer, but because it took time for you to use those, because those are your worst embryos. You're getting to the bottom, right? So at the end of the donut box, all that's left is jellies. You use your best ones first. So it just makes sense that, yes, the ones that have been frozen longer aren't going to do as well, but not because they're not good, but because those are the lowest quality graded embryos, because you use them last. Now, some people may be listening, going, okay, but why would people freeze stuff? I mean, should I be doing this? Well, it depends. When it comes to sperm, there are many reasons. Maybe its cancer, maybe youre going to be gone, such as military deployment, or maybe youre going to get a vasectomy and youre just worried about, hey, what if I change my mind? So its not bad for sperm as kind of a backup plan. And it's so easy that a lot of people do it. Now, eggs are a little bit different. There's a little bit more work you have to go through. So when you're freezing eggs is either because you're preserving fertility, the other situation is maybe you are going to undergo some type of cancer treatment, undergoing chemotherapy. And so you may want to freeze your eggs before treatment. Even if the chances of hurting your egs might be low, you don't want to take a chance. Now, the reason we freeze embryos is because it allows us to do several things. One is we can then do genetic testing while we wait for the results to come back. The Embros are frozen for us to then do a transfer. The other benefit of freezing embryos is it allows us to then have future chances. So you can go through one retrieval and then potentially have multiple transfers for multiple children. It also allows flexible timing. Maybe you want to freeze your embryos now because youre 38 and you dont want to wait till 40, but youre not ready to have kids yet. You could freeze those embryos, wait a couple years, and then do the transfer when it's ready for you. Now, one of my favorite things that comes up is how do we store them? A lot of people go, well, what if the power goes out? That's a great question. But unlike your freezer, there is no power needed to keep your eggs, embryos and sperm secure. And that's because instead we use tanks filled with liquid nitrogen. And we just make sure we top the liquid nitrogen off to keep it cold. So whether the power goes out or not, it's always going to be cold. Now, these tanks are monitored so that way they have alarms on them. There's backup systems. That way we know if for some reason the liquid nitrogen is dropping, and that's how we know to make sure to keep it going. Some places like our own have tanks that actually autopf fill. So for ones that are, let's say, for long term storage, it's constantly filling it so we don't have to fill it and alarms are built in. So in summary, the takeaways from today's podcast are freezing is safe and effective thanks to vitrification. Now, when it comes to sperm, we still use slow freezing because it's the best method when it comes to survival rates. The rates are excellent and even though sperm may have poorr survival rates because there is so much sperm, we still get the sperm we need. The last caveats are even though you can freeze sperm, it'hard to pull it because you end up losing so much. You cant pull a bunch of sperm for an iui. And then the very last thing is ah a no. It doesnt t matter how much time your eggs or your embryos are. Sperm are frozen. Biology is pause. So time is not your enemy. I want to thank Arion Smith for giving us this topic and for the questions he had. These are the best topics to do because it's coming straight from you guys. And so if any of you have questions or topics you want me to do, send an email to mebftirectionfertility.com I'll be more than happy to make a podcast about it. If you're considering freezing your sperm, eggs or embryos, or have you'been wondering how it might fit into your journey, talk to your doctor about your specific case. As always, I greatly appreciate everyone to listen to this podcast. If you found this podcast episode helpful, or maybe you know someone who may be help before, please share it with them. Give us a five star review on your favorite medium, but most of all keep coming back. If you enjoyed this episode, dont forget to subscribe so you never miss another episode. I look forward to talking to you again next week on Talk About Fertility Tuesday.