Do blastocysts have better quality than oogenesis embryos? Let’s take an example, we can consider blastocysts as “high school students” and oogenesis embryos as “elementary school students”, and compare the probability of going to college between them. However, not every high school student can go to college, and elementary school students are not necessarily worse than high school students in the future, and there is even a possibility that all of them can go to college. Therefore, in terms of probability, the overall developmental potential of blastocysts is higher than that of oogenesis embryos. What is the difference between oogenic embryos and blastocysts? Firstly, in terms of time (the day of egg collection is D0), a cleavage-stage embryo is an embryo on day 2-3 after egg collection, while a blastocyst is an embryo on day 5-7 after egg collection; secondly, spatially, a cleavage-stage embryo is located in the fallopian tube, while a blastocyst is located in the uterus; thirdly, morphologically, a cleavage-stage embryo has a low cell count, with day 2 embryos generally being around 4 cells and day 3 embryos generally being around 8- Fourth, in terms of regulation of gene expression, the development of the blastocyst depends mainly on the genetic material stored in the egg. Fourth, in terms of gene expression regulation, the development of the embryo at the oogenesis stage relies mainly on the genetic material stored in the egg, and this stage is supported by the strength of the “mother”, while the blastocyst undergoes a transition from maternal to syngene regulation, and relies on the strength of both “parents” to grow and develop. Therefore, only good eggs with good sperm have the potential to develop into blastocysts. Is it better to transfer oogenic embryos or blastocysts for embryo transfer? First, the selection power of high-quality embryos: Currently, the assessment of the developmental power of both types of embryos is mostly based on morphological scores, which are subject to some bias. Blastocysts have a higher developmental potential for embryo implantation after the test of blastocyst culture because they have undergone a secondary screening. However, with the advancement of technology and the improvement of various testing methods, embryologists have been able to accurately screen for embryos with high developmental potential at the oogenesis stage. Second, success rate: According to reports, the average live birth rate of an oogenesis embryo transfer is about 30-35%, while the live birth rate of a blastocyst can reach 50-60%. However, the success rate here is only for a single transfer cycle, and there is little difference in the cumulative success rate (fresh egg retrieval transfer cycle + thawed embryo transfer cycle). Third, the risk of blastocyst culture: blastocysts have a lower rate of usable embryos than oogenesis embryos due to self-screening and elimination during the blastocyst culture period. In addition, although the developmental potential of blastocysts is high, not every embryo can form a blastocyst, and even high-quality embryos have the possibility of no blastocyst formation, and there is a risk of no embryos available for transfer. Fourth, offspring safety: The current in vitro culture environment is not yet at the same level as in vivo, so the embryos may be subjected to various stresses during blastocyst culture, and some studies have shown that the birth weight of blastocyst cultured offspring is heavy, but it is not yet possible to answer this question conclusively whether this increases susceptibility to adult-onset diseases. Overall, there are advantages and disadvantages to choosing between oogenic and blastocyst transfer, and it is best to choose the right transfer option for your conditions.