One at a Time: Why Single Embryo Transfers Win the Odds

In this episode of Taco Bout Fertility Tuesday, Dr. Mark Amols explores why transferring one embryo at a time often leads to better outcomes than transferring two simultaneously. Building on previous discussions about statistics and probabilities, this episode dives into the math, biology, and risks associated with multiple embryo transfers. Dr. Amols also addresses misconceptions, explains the factors influencing cumulative success rates, and highlights situations where single or double embryo transfers may be appropriate. Tune in to learn how understanding these principles can maximize your chances of achieving a healthy pregnancy.

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Transcript

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Today we talk about why slow and steady wins the race when it comes to single embryo transfers. I'm, Dr. Mark Amols and this is Taco about Fertility Tuesday. When it comes to embryos, one might be the loneliest number, but it's also the smartest number if you're aiming for the best chances as success. In last week's episode, we touched on the statistics infertility and how this idea that one embryo being transferred consecutively can actually have a higher chance than putting twomers back at the same time. Well, in this week's episode we're going to continue the conversation about statistics and ferility, but specifically about this one topic of why it's always better to put back one embryo versus two in most situations. In addition, in 2019 we explored this question with that episode, how many embryos should I transfer? But today we're going to dig deeper than before, reaffirming some of the past device, but also clarifying why transferring one embryo at a time may often be the best choice, especially if you only have two embryos to work with. There are two main reasons for discussing this topic again. The first is there has been a big push in the community to force people to only put back one embryo. And as I talked about in my prior episode, we would allow people to put back two embryos because I believe people should have the choice. Unfortunately, this has becoming even harder nowadays because now insurances are pulling contracts if people are doing two embryo transfers that are not under the guidelines of the American SOC reproductive medicines recommendations. And so you're going to find that anywhere you go, it's going to be very difficult in certain situations to put back more than one embryo. But additionally, things have changed. The quality of IVF has gone up and with science, when things change, we make adjustments. Everything I talked about in that previous episode is still true. But in today's episode we're going to talk about why they want you to only put back one embryo and why mathematically it actually does improve your chances over two embryos in certain situations. Now, un last week's episode we discussed how in probability there's a thing called cumulative rate. And that is where when you add another chance, it doesn't just add up directly. Meaning if your chances are 60%, putting two embryos back does not give you 120% because you can't have over 100%. Therefore, that means if you put two embros back, your chances won't be 120% but will actually be around 84%. Now it's important to understand that when we're talking about chances, we're talking about it's a higher chance of getting at least one embryo to implant and have live birth. The 84% does not mean your chances of them both taking, such as twins. The problem with this calculation is it's not taking into account things that can occur, such as subcharic hemorrhages, ectopic pregnancies, or even having higher complications with twins. And so when you take those into account, what you find is, is that by putting back two euloid embryos, you actually have a lower chance than putting back one euuplooid embryo consecutively. Now, what it doesn't mean is it doesn't mean that putting back one embryo is better than two. I've heard other doctors or people say this, and that's ridiculous. Of course there's a higher chance with two embryos. But what isn't obvious is that by putting one embryo back and then let's say that not working and put another embryo back, you actually have a higher cumulative chance than if you go and put both embryos back at the same time. And this increase can be significant somewhere between about 3, even as high as 10% difference. And so if you think about, think of all the things you do just to improve your chances, a percent or two, even embryo glue doesn't improve your chances that much. Clinics that you go to to get increased chances might be that different. And so in reality, the point here is that if your goal is to have the highest chance and you want to have the highest chance of come in the way with the live birth, you are always better to put back one at a time. If you have two embryos, then putting both embryos back at the exact same time. Now, my position hasn't changed. There is definitely some cases of where two embryos make sense. And if you have a lot of embryos and you have a clinic that's able to do that, because maybe they're a cash only clinic and so they don't have to worry about losing contracts, it's something to talk them about. Now, the situations where it's still appropriate is where if someone has, for example, low quality embryos, so let's say they're not tested and maybe they're poor quality, or day seven embryos, it's not unreasonable to put too bad because we know the actual potential of those embryos are already low. The same would be true with say, embryos that are mosaic or high mosaic. Another situation is when we're talking about women who are more mature and did not do PGT testing, those embryos have a lower chance of being euoid and therefore it's not unreasonable to put back more than one. Now there are some places that still do cleavage stage embryos and in that situation too it makes sense to put back more than one when you start advancing in age. But very few clicks now are doing cleavage stage embryos. And so I'm keeping this mostly to blastocyst when I talk about one versus two. So let's talk about each scenario. If you are under 35 in almost everyenario, if it's your first transfer, whether it's a cleavage stage embryo or blastocyst, it's recommended to put back one embryo. ASRM does have a side note that says if the embryos are not euoid or favorable, then in that situation it's not unreasonable to put back two, but never more than two in that situation. This again is going to be very poor quality embryos. Embryos that are mosaic or like we talked about day seven embryos. If you are age 35 to 37, everything kind of stays the same. It's still recommended by the American side of reproductive medicine to put back one embryo whether they're Cleveland stage or blastocyst stage if they're euoid or not euploid as long as the embryo is favorable. Now if they're blastocyst and they're not favorable, they do not recommend more than two at any time. If it's Cleveland stage but it's not favorable, then you can go up to three but not more than that. When it comes to 38 and 40 age group, if you are using cleavage stage embryos, it's recommended that even if they are favorable, not having more than three, if it's EUoID only one, and if they're not favorable, then up to four but no more. Now when comes to blastocyst, it's recommended again if you ploed only one embryo and if it's favorable but let's say not tested up to two and if it's not favorable such as we said day seven embryos, even up to three, but that's assuming not eu ploid, the last category is going to be 41 and above. And basically the same holds true. If it is a euloid embryo you would put back one embryo whether it's cleavage stage or blastocyst. If it is not tested then you can put up to four at 41 to 42 and not more. And then again if it's not favorable and again not being euoid, you could even theoret put up to five, but not more. Now, when comes to blastocyst, the rule remains the same. If it's euoid, one embryo now, if it's not tested up to three is reasonable. And if it is not euoid and not favorable, still only three. And the big reason for this, why it doesn't go as much in blastoc, is because they have already undergone the attrition rate that should occur to remove a lot of the abnormal embryos. And so it's dangerous to put back too many blastocystss. Whereas with cleavage stage embryos, there's so many, abnormal still embryos are in there that you can put back more. Now, another important piece to understand is when we're talking about this, we're talking about first embryo transfers. No one is saying that if you have had multiple failed embryo transfers or in certain situations, you cannot put back more than one embryo. Even if you have euloid embryos, if it's been failing and failing and failing, it's not unreasonable to put back more than one. What this is talking about is at least your first two transfers should always be single embryo if they're euoid. And then after that is when you can start to look at potentially putting back more than one. And this is for the benefit of increasing your chances of coming away with a pregnancy. And this is because if you put two embryos back and you assume that nothing is going to happen to either those embryos, yes, things may go fine. But by putting two embryos in there, you now take twice the risk of something happening to one which could theoretically affect the other embryo and you would lose both embryos. A matter of fact, as many people know, you can do a transfer. It just doesn't work. And the reason why is there could be something, let's say at the uterus or some condition at that time, maybe you got a fever, and now if all your eggs in one basket, you'lose them all. This is why it's always best to put back one embryo when it's euloid. Now, why are the insuranceances pushing this so much? Is that they just don't want people to have choice? Well, not exactly as you would imagine. It has to do with finances. When you have a single embryo and you put it back and you get a single live birth, the cost to insurances is about $20,000 or less. As soon as you get twins, that cost goes up to at least $100,000, more than five times the cost of, just a single delivery. And if you get triplets, it could be anywhere between about 500,000 do to a million dollars in cost due to all the care that has to be for the babies. And that's because multiples end up coming earlier. You get preterm labor and can actually lead to some complications. So their reasoning isn't unfair, it's just frustrating because we're adults and should be able to make decisions. In the past episode I discussed that by putting one embryo back, your risk of twins is so small it's well below 1%. But by putting two duploid embryos back, you increase your chance of twins, sometimes over 40%. Which means you take almost an 80 to 100 times more risk of having twins, but only increase your pregnancy chances from 60% of a live birth to just 84. And when taking into account the risk even less than four, close to around 75 up to around 80. So as you can see, you don't get much benefit, but you get a lot more risk. Now, as I always say, these decisions are personal and depend on your unique circumstances. And you should talk to your physician about this. You should always feel free to ask if you can put 2 embr back. But I wanted you to understand why many clinics are no longer doing it and even the ones who are okay with doing it are now being forced to not do it. But I always like to look at all sides and like I said, financially the insurances are correct. It is much more cost effective for them to only put one back. And for patients, it also is more effective to come away with a live birth. And like I said, we do some pretty crazy things just to even increase our chances 1%. I see patients take 8, 10 bottles of different pills just to improve their chances a tiny bit. So in reality, if the goal is to have a live birth, then reality, one embryo will increase your dreams of having that live birth. Where I think this matters the most is when you only have two embryos. I would never recommend anyone to put both embryos back at the same time because you only get one chance when you do that versus two chances when you do it one at a time. Like I said, you don't know what can happen. You can then begin a fever the next day and lose the pregnancies. Maybe in the middle will transfer, you cough and all of a sudden the catheter hits the top of the uterus and doesn't work. So especially in the situation where you have two embryos and both are EUoID, I would always recommend one at a time. And if you're younger, if not tested, I would still recommend that. But as I mentioned, there are situations where you are not testing embryos, where patients are more mature, where the embryo quality is poor, or even when implantation rates are low that it is reasonable to put back more than one. So it's not an always put back one, it's just when first starting, it's reasonable to only put back one to improve your chances of success. And if your doctor recommends putting back two, it doesn't mean that they aren't doing the right thing, it means that they believe in that situation that's the best thing for you. And I would take their advice. When I record these podcasts, I don't know your exact situation and so everything I'm talking about is somewhat generic. So again, it's always important to talk to your doctor and realize that your situation might be unique. So in summary, single embryo transfers give better cumulative success and minimize the risk. So even if it feels like two emeralds would give better odds, the math and biology tell a different story. So just like last episode, understanding probability can lead to better decision making. Hopefully Ivet bored you guys with these two episodes discussing probability and math and hopefully this was helpful to some people. If you liked this episode and like the show, please tell your friends about us and as always, give us a five star review on your favorite medium. If you have any suggestions for the show, please send us a message atbftirectionffertility.com we'll be more than happy to try and make an episode on that. I look forward to talking you again next week on Taco Bel Fertility Tuesday.