What are pros and cons of a single embryo transfer?

I can’t really see any advantage of transferring more than one embryo, other than shortening the time to pregnancy – obviously at the risk of that being a twin pregnancy. I think our role as fertility doctors is not just trying to get pregnant at any cost. We have to focus on maximizing the chances of obtaining healthy babies. And the easiest way of doing that is having single pregnancies. This is why one of our general policies is to carry out single embryo transfers in all egg donation cycles in which the quality of the embryos is going to be good.

In all the IVF cycles in which we are transferring genetically normal embryos to patients who have pre-implantation genetic screening done. On top of that, we know that the embryos do not interact with each other when we transfer them together: they don’t help each other, they don’t disturb each other. It means that if you transfer two embryos, you are going to have higher pregnancy rates in that transfer – but the overall pregnancy rate of the cycle, the so-called ‘cumulative pregnancy rate’, is going to be the same.

The only drawback of transferring one embryo each time is that you may need more attempts to reach that overall pregnancy rate. But it is not going to change at all. So we have to balance the risks very well that are involved in transferring two embryos and recommend a single embryo transfer whenever we can.

We don’t eliminate the risk of multiple pregnancy but drastically lower the risk of multiple pregnancy. We know all that the multiple pregnancy in itself can be a high risk pregnancy. Pregnancies resulted from IVF are always very precious pregnancies, so we want to try and improve the chances of that patient having a healthy single live birth because the moment they have multiple pregnancy they are at additional risk of miscarriage as well and potentially, if there is no higher risk of miscarriage, is a higher risk that the babies are born prematurely and be spending more in the neonatal unit, so we way up those risks very very carefully. As a matter of rule, I always say it is better to play it safe rather than being sorry. My advice is always to put a single embryo transfer. Yes, the pressure should be on me as an embryologist, to select the right embryo, even if this means using technology such as genetic screening or genetic testing embryos. We should know which one is the golden embryo rather than putting multiple embryos back. That is the concept which doctors and embryologists should be working on.

The goal of IVF should be a healthy mother expecting one baby. Nowadays, with the growing success rate of IVF and all the possible methods in embryology laboratories, the goal is a single embryo transfer. Still, there are situations when we use two embryos for transfer and we know that it has a slightly higher success rate but of course, there is a risk of multiple pregnancy which carries some risk. So, the pros of a single embryo transfer are that there is really a low chance for a twin pregnancy but there could also be a little lower chance for pregnancy at all. So, we strongly recommend elective single embryo transfer in fresh or frozen transfer.

After several years of experience in the field of reproductive medicine, there has been a change in the tendency of the number of embryos that we transfer. Nowadays, the global tendency is to transfer one single embryo. Especially when we are transferring the embryos at the stage of blastocysts, the quality of the embryo is usually good.

Therefore, the likelihood of pregnancy is good as well. One of the most important things that we have to remember when we’re doing fertility treatment is that our role is not only to get a patient pregnant but also to make sure that she has a safe pregnancy. That she and the baby are healthy along with the pregnancy and that its outcome is good as well. We know for sure that twin pregnancy and multiple pregnancies are much riskier than singleton pregnancies from the obstetrical perspective. There is a much higher risk of preeclampsia, gestational diabetes, pre-term delivery, and other obstetrical complications along with the pregnancy. Therefore, the single embryo transfer would be the recommended kind of transfer.

Nevertheless, there are some specific cases in which we may consider transferring two embryos, especially in cases when we have had several failures before or when we know that the quality of the embryos is not the best. But generally, to reduce as much as possible the risks of complications along with the pregnancy and maximize the chance of having a healthy baby, a single embryo transfer would be advised.

When we have many high-quality embryos for transfer, some patients would ask: what should they do? Should we try a single embryo transfer? Should we try a double embryo transfer? What is the option to try to increase as much as possible the pregnancy rate and the evolving pregnancy rate and having a baby at home? So transferring many embryos or two embryos at the same time might increase the possibility a little of a positive pregnancy test, but it won’t increase the possibility of a baby at home, seeing that when we transfer two embryos, we do have a higher miscarriage rate.

So with a single embryo transfer and a double embryo transfer, we will get exactly the same newborn rate. And that’s what we want, a healthy baby at home. Of course, when we do a single embryo transfer, and we do have the opportunity to freeze another blastocyst or some other blastocysts, if we get a negative pregnancy test, we do have the possibility of a further embryo transfer and increase the cumulative pregnancy rate. So in the first transfer, we might be at 60% of patients that do get a positive.

If they get a negative the month after the first transfer, we might have the possibility again to get 60% of positive pregnancy rate, which means that after two cycles, we might already have up to 85% of patients that have had a positive. If we transfer both embryos, at the same time, we might get up to 65% positive, but we will never go up to this 85% that we get with a single embryo transfer, one per month. So we would strongly recommend going for a single embryo transfer when we do have many high-quality blastocysts.

In assisted reproduction, we believe it is better to have a pregnancy with only one baby. If we have twins, we have more possibilities of some problems, like hypertension and diabetes in the pregnancy or premature delivery. So we believe it is better to do a single embryo transfer if we have high-quality embryos.

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