Most IVF couples face a problem when the sperm and eggs are removed and developed into embryos by in vitro fertilization (especially if more eggs are obtained and more embryos are paired), they have to face a question on the third day, whether to transfer fresh embryos? Should we keep the remaining embryos in blastocysts or freeze them to create more transfer opportunities? Since many patients have to make a choice at that time, it can be rather torn. Usually embryos can be transferred by the third day of culture, and if you continue to culture and raise the embryos until the fifth or sixth day when they are still alive and developing well, they are what we call blastocysts. So is it better to transfer day 3 embryos or to transfer blastocysts? If transfer is not possible at that time (e.g. high progesterone, ovarian hyperstimulation, etc.), is it better to freeze all the embryos or to raise them to blastocysts and then freeze them? The current trend is that more and more fertility centers are recommending the transfer of embryos after they are cultured into blastocysts, and only one blastocyst (single blastocyst transfer), because transferring two blastocysts increases the chances of twin and multiple births, which can have a negative impact on both the mother and the fetus. First of all, the success rate of transferring blastocysts is higher than transferring third day embryos. Here is a simple example, when planting vegetables is first in a place to cultivate seedlings, then transplanting the kind of seedlings easier to root and germinate it, if the third day are about the same growth, may be observed for two days, until five or six days may grow unevenly, then put the good growth of seedlings into the soil will be easier to root and germinate. This is the same reason as embryo culture transfer, if the embryo can be raised to the fifth or sixth day, it proves that its development potential is better, then the chances of pregnancy after transfer are high. Of course if better embryos (grade 2 or higher) are evident by day three then the success rate after transfer is also higher. This has the advantage of reducing unnecessary freezing costs and trying to achieve the maximum success rate with the least number of transfers. The other extreme way is to freeze all embryos, then the number of times you transfer will increase greatly and it seems to increase the success rate (cumulative success rate), but if the embryos are not of good quality freezing will aggravate the embryo damage and may even downgrade, and the survival rate after thawing is also low, and multiple unsuccessful transfers will affect your confidence and mood. Of course, there are also risks in in vitro culture, that is, if the embryos are not raised into blastocysts, there may be no chance of transfer, and the embryos may be damaged by the change of culture fluid, PH value and CO2 concentration in the process of embryo culture, after all, the embryos are most suitable for their growth and development in the body. However, with the development of technology, the laboratory conditions and culture environment have been greatly improved, and this damage will be less and less. In conclusion, if there are good quality embryos (grade 2 or above) on the third day, then we can consider transferring superior embryos, if not, we suggest that it is better to raise blastocysts, as the success rate of transferring will be higher if the embryos are raised successfully, but of course, we have to take a certain risk that the embryos will not be raised successfully and no embryos will be available for transfer. However, if the blastocyst is not raised, the chances of pregnancy will be very low and the risk of miscarriage will be higher even after the transfer. For older patients with poor ovarian function, if there are fewer embryos, it is more important to raise blastocysts to increase the success rate of a single transfer and interrupt the cycle if it is unsuccessful and wait for the next cycle. If repeatedly transferring embryos in unsuccessful, it will be a big blow to your financial and psychological and physical tolerance.