From our point of view, the best day for embryo transfer will be either day five or day 6, because it’s the moment when we will find embryos at the blastocyst stage. So, day 6 embryos are also a good option for transfer. Sometimes, they develop a bit slower, so we have to give them their time. We will prioritize day 5 embryos, but of course, if a patient’s embryos reach day six, we will consider them for transfer anyway.
I suppose the question means: should we transfer a Day 3 embryo or a Day 5 embryo? Usually I would say, if the embryos allow, blastocyst transfer is the best time to transfer the embryo but as I said earlier, not all patients are ideal candidates to wait for blastocyst transfer. Sometimes if a patient only has one embryo, that embryo in my opinion is better off being back in the natural incubator rather than the artificial incubator which can be an additional layer of stress for that embryo as well. My concept is to put it back in the natural environment unless you have an option or a choice with other embryos.
Here, at Clinica Tambre we always do the embryo transfer on day 5 of embryo development when the embryo reaches the blastocyst stage. We know that over 50% of the embryos stop development before reaching the blastocyst stage. Blastocysts have a very high implantation rate. Our incubators simulate the uterine environment so that the embryos are safe during their development. Monitoring the embryos until day 5 gives our embryologists the possibility to choose the best embryo with the highest success rate for your transfer.
There is not such a thing generally, as the best day to do the embryo transfer. The best day to do the embryo transfer is personalized. This depends on each case, of course, in ideal circumstances, the best thing would be to do an embryo transfer on day 5. This is normal if you think about it, we leave embryos to grow outside the body, so actually, there is a natural selection. Many times between day 3 and day 5, lots of embryos do not survive, and this means in most of the cases that they don’t have the potential to survive because they’ve got chromosomal abnormalities. If an embryo reaches day 5, it has more chances of being chromosomally normal rather than if we transfer it on day 3. This is why the best thing and the target behind IVF are to always try to get to the blastocyst stage in a laboratory, of course, the one that can support nice cultures to develop the embryos.
By any means, though sometimes, it can be better to transfer on day 3, and this depends on the amount and the quality of the embryos. It also depends on previous attempts and previous failures, and sometimes we can even choose to transfer both on day 3 and day 5. We need to know if we’re going to answer the question, which day is the best to transfer an embryo, this depends again on the case, but generally, it’s always better if we can transfer a blastocyst.
Without any doubt, the best day for an embryo transfer is day 5. The main reason for that is that the most critical day for the embryos is day 4 to day 5. This is when it’s more likely that any embryo can get blocked. If you transfer it before that, if you transfer it on day 2 or day 3, you may be transferring perfect embryos that are not going to become blastocysts. You may give this kind of false impression to the patient that it has been a good cycle, but if you had the quality of these embryos properly checked, sometimes you could find out that the quality was far from being good. This is important because sometimes, I’ve seen patients who have had several cycles in which the embryos have been transferred on day 2 or day 3 that have been requested to undergo a long and expensive list of tests to check if there was something wrong with the uterus and implantation.
We lack the information about the real quality of these embryos because if you had left them in culture, they probably wouldn’t have become blastocysts. Even when there is only one single embryo, we recommend taking it to a day 5, unless the patient wants to save the money of the cost of the blastocyst and wants it to be transferred before. Even if the embryo does not make it to blastocyst, and we end up without a transfer, that’s much better for the patient’s future than if we transfer on day 2 or day 3. At least, we are going to be sure that the problem is in the embryo, and if that patient wants to improve the success rate, they may have to change something, but it won’t be necessary to start checking if there is anything wrong with the uterus side.
