Embryo transfer is the last and most important step in IVF and is an important factor in the success rate of IVF. Under normal physiological conditions, embryos will enter the uterus when they develop into mulberry embryos to blastocyst stage 4-5 days after ovulation, but in IVF, due to the limitation of culture conditions, the time of embryo transfer varies greatly, most of the embryos are transferred at the oogenesis stage, but in recent years, with the gradual optimization of the blastocyst in vitro culture system, more and more centers are culturing embryos to blastocyst stage in vitro before transfer, so whether it is Is it better to transfer D3 embryos or D5 embryos? First of all, day 3 embryos are cultured in vitro for a shorter period of time, which allows for more quality embryos, but the degree of selection of embryos is limited, the morphology of the embryos does not necessarily reflect the viability of the embryos, and the embryos enter the uterine cavity too early compared to normal physiological conditions, and the development of the endometrium is not synchronized, and the embryos are suspended in the uterine cavity for a period of time before implantation, thus requiring the selection of 2 embryos for transfer increasing the risk of multiple risk of multiple pregnancies. The prolonged blastocyst culture results in the natural elimination of some chromosomally abnormal and poor quality embryos in vitro, and the prolonged culture runs the risk of having no available embryos for patients with a small number of embryos, while for patients who obtain a large number of embryos it is the best of the best and improves embryo-endometrial synchronization, which is more in line with the physiological process of implantation The embryos at the blastocyst stage are larger than those at the oogenesis stage and are more difficult to move towards the fallopian tube, which reduces the incidence of ectopic pregnancy; the improved implantation rate makes single blastocyst transfer possible, thus avoiding the transfer of multiple embryos The risk of multiple pregnancies can be avoided. As we can see from the above, there are advantages and disadvantages of different stages of embryo transfer. Whether to transfer day 3 embryos or day 5 blastocysts should vary from patient to patient, and the doctor will evaluate the patient’s condition, including endometrium, hormone levels, as well as the number of embryos and their development.