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The number of embryos to be transferred depends a lot on each individual case. It is not the same when you are transferring a good blastocyst to a young couple or when you are transferring good blastocysts coming from egg donation to a 43-year-old woman or where you are transferring a blastocyst created with their own eggs of a 44-year-old patient.
The main decision or the main things that we must bear in mind when we are deciding the number of embryos that we are going to transfer is the age of the woman, medical background, it could be different if it’s the first attempt or if they have been through 2 or 3 rounds of IVF and also the quality of the embryos and the number of embryos that you have.
Indeed, sometimes embryos that look great may not succeed, and embryos that don’t look so good may be successful, but if you have a lot of good quality embryos, we tend to be more conservative and transfer only one blastocyst especially, if the patient is young.
If we have 2 or 3 lovely blastocysts and the patient is 43, we know that the risk of these embryos having genetic issues because of the patient’s age is high. Then we may assume the risk of transferring 2, or even 3, so it’s a very individualized and personalized decision based on the different factors I’ve mentioned before.
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According to NICE guidelines and HFEA regulations, we are bound to have a number of embryos. We can basically have two names: “SET”, an actual acronym of “a single embryo transfer”, and “DET” (“double embryo transfer”). Why is that? It depends on so many things. One of them is your age and this is the most important thing. The actual age is the denominator to tell me how many embryos I should transfer. Usually, in general terms, if you are until 37-38, we can only place one embryo. From 37-38 onwards up to 40, we can transfer 2 embryos, especially if you had a failed IVF before. So a previous history is obviously a guide for us. Even if someone is young but she had 2 or 3 single embryo transfers failed, we can have some sort of exceptional circumstances and transfer maybe a higher number of embryos.
Also, there is the quality of the embryo. The embryo quality is of utmost importance regarding the decision-making of transferring 1 or 2 embryos. If someone has a very high-grade blastocyst, we would always recommend going for 1, that’s for sure. However, with lesser grade embryos, you can argue to transfer more than 1. So that’s another sort of parameter.
Day 3 or day 5? We know that day 3 embryos do not have the same implantation potential as day 5 embryos. Taking this argument, we can always decide whether it is advisable to transfer 1 or 2 embryos.
If you’re having an egg donation cycle, the recommendation is to have 1 embryo transferred. Why? Because it typically works for your best interest. I’m talking about the age category between 40 and 50, if you’re having egg donation for this reason. A single pregnancy is always safer than a twin pregnancy. I know there are a lot of arguments and couples who wish to have their family complete in one step, like having twins. I have this a lot. However, it is not easy and recommended for safety reasons to have twins. I know it is advantageous for you, however, it gets a lot of risks for you and NHS. So as I said, what’s important is your age, the quality of the embryo, whether it is day 3 or day 5 and if this is an egg donation cycle or a fresh IVF transfer.
It goes the same with a frozen embryo transfer (FET). If you are within the young patients’ category, together with a high-grade blastocyst that was frozen, the recommendation is to have only 1 transferred. So we aim towards 1 embryo – but obviously, with age and grading, we go for 2, and, under exceptional circumstances, we can transfer 3. The transfer of 3 embryos also depends on whether it is day 3 or day 5 and the age. Above 43 or 44, we could negotiate to have 3 embryos.
Transferring 2 or 3 embryos to a young patient is obsolete now in this country, because of the risk of multiple pregnancies, whether twins or triplets. It is not advisable to have this kind of risk for someone who could end up with a single-term pregnancy. We always say that a healthy singleton pregnancy is far better than having any complications from twins or triplets pregnancy.
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My opinion on this is that we should be using technology to select the best embryo to transfer rather than putting multiple embryos back. I’m of the opinion that the maximum number of embryos I would ever want to transfer in a patient is two, not more than two, even if the patient is over 40 but even when we transfer two embryos back, we should be in a position to counsel the patients very adequately about the risk of multiple pregnancy and it has to be a decision taken very carefully after a lot of consideration and assessing the risks on a case-by-case basis.
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The optimal number of embryos for transfer is one, only one. There are two reasons. Firstly, safety and to avoid the risk of twins. Secondly, when we do the transfer, we can measure the thickness of the endometrium, vascularization of the endometrium, but we can’t measure if the endometrium is really able to accept the embryo. The testing of this is very problematic, very difficult. If we transfer more embryos, for example, 2-3 embryos, and the endometrium is not prepared to accept the embryos, there will be no implantation.
We call it the implantation window, but unfortunately, we can’t test it. We can’t do bedside testing immediately after the transfer. Sometimes, some patients are not able to accept the embryo. There is some bad timing of the transfer, and it’s necessary to make better timing of the transfer. But we can’t test it quickly. It is a very complicated examination. If you are transferring embryos one by one, you are lowering the risk. Transferring two embryos at once does not mean double chances for implantation. For example, in egg donation, it’s a 50% chance for one blastocyst to have a take-home baby. If you transfer two blastocysts, there is only a 60% of chance having a take-home baby.
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Normally, in every country, the number of transferred embryos is restricted by the law. In Turkey, in our country, for women under 35, single embryo transfer is allowed for the first two trials. After the third trial, even though you are under 35, you can have two embryos transferred. For women over 35 years old, only two embryos and not more can be transferred.
If there are any extra embryos, they need to be frozen and stored on the patient’s request. The optimal number according to me is two. Because if you transfer only one embryo, the expected success rate is 30-35%, but if you transfer two embryos, automatically the success rate will rise to 50-60%. Most of the time, this is a process not supported by the state and the patients will pay from their pockets, so we aim to offer the best, quick, and most economical way to the patients. Between 30-35% and 60%, there’s approximately a double percentage difference. I’m sharing this with the patients, and if they wish I can transfer one or two embryos, but not more. Our biggest fear is multiple pregnancies and as a gynecologist, I don’t want to cause any multiple pregnancies for the patient.
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Yes, this is a very important question, particularly for safety reasons. You all know that in the last 10 years, there’s been a trend towards transferring only one embryo at a time. It’s also known as elective single embryo transfer. The reason why all the specialists like myself moved towards that trend, is because primarily, we want to reduce the chances of having multiple births. And not just twins, but also triplets or quadruplets, which was very common in the past. So it’s a safety reason.
But also, because the technology and the IVF technology has improved over the last 10 years in terms of culture conditions, the drugs that we use, and the equipment that we use. The success rate seems to be very similar whether we transfer one embryo or two embryos. So the only potential side effect is that if you transfer more than one embryo, so two embryos, then you have probably a 40-50% chance of having a multiple pregnancy which can be quite problematic not just for the mother, but also for the babies. It can also increase the risk of miscarriage to start with, but also going through the pregnancy, the risk of introducing growth restriction where the babies are not growing at the speed that they should, or causing preterm labour when the babies are born prematurely. We need to be conscious about all these potential complications, and that’s why the trend nowadays is to transfer one embryo at a time.
Obviously, this very much depends on the age of the patient, the quality of the embryos, the previous obstetrics history, or previously failed IVF treatment. There are lots of indications that we consider and discuss with a patient. But the standardized practice, at least in Europe, is to go towards the transfer of one embryo to be safe.
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The optimum number of embryos to transfer will differ for each patient and each cycle, to balance both a good chance of success and minimize the risk of a multiple pregnancy. The HFEA has stated that fertility clinics should keep their multiple birth rate below 10% each year.
The safest is to transfer embryos one at a time due to the increased risk of multiple pregnancies on both the mother and babies. All fertility clinics within the UK will have a Multiple Birth Minimisation Strategy to highlight which patients will be better off transferring a single embryo in their treatment cycles. Usually these are women having their first cycle of IVF or ICSI, those aged 37 or under and those using donated eggs or embryos.
Other patients deemed to have a lower chance of success and therefore low risk of multiple pregnancy may be advised to transfer two embryos, to increase the chance of them having one healthy baby from the treatment cycle. These may be women having treatment with eggs aged 38 or over, or who have had multiple failed treatment cycles. Speak with your consultant and embryologists for the recommended number of embryos to transfer in your treatment cycles, as the advice may change each time.
