With the development of assisted reproduction technology, the success rate of IVF has been increasing, and the pregnancy rate of Day 3 (D3) embryos transferred at home and abroad is about 40~50%. Currently, the screening of D3 embryos is mainly done through morphological observation under a microscope to select the “most beautiful” embryos for transfer. However, “you can’t judge a book by its cover”, and there are limitations in selecting the embryos with the highest developmental potential by purely utilizing morphological evaluation. One of the trends in IVF is to go back to nature and try to mimic normal in vivo fertilization. Normally, D3 embryos still travel through the fallopian tubes, and only those that have developed to the blastocyst stage make it to the uterine cavity for implantation. IVF D3 transfer is the transfer of D3 embryos into the uterine cavity, at this time the uterine cavity is not ready to accept the embryos for implantation, the embryos will wander in the uterine cavity, and may even wander into the fallopian tubes. If both fallopian tubes are blocked at the proximal end, the environment of the uterine cavity is not suitable for the development of the embryo at the cleavage stage, which will result in a low pregnancy rate; if the fallopian tubes are open or blocked at the distal end, and the embryo wanders to the fallopian tubes can not wander back to walk to the uterine cavity in a certain period of time, then ectopic pregnancy is likely to occur. After blastocyst transfer, the blastocysts travel directly in the uterine cavity to plant, greatly reducing the occurrence of ectopic pregnancy. Therefore, it is in accordance with the law of nature to continue culturing embryos to blastocyst stage and then transferring or freezing them. At the same time, continued culturing will eliminate the embryos with poor quality and development potential, thus improving the implantation rate and clinical pregnancy rate, avoiding the cost of repeated transfers, and achieving the ultimate goal of “giving birth to a healthy child”. What kind of patients are suitable for blastocyst culture? 1.Relatively young age, good ovarian reserve, ideal number of eggs, the risk of blastocyst culture is smaller. 2.After double proximal tubal obstruction or double salpingo-oophorectomy, the uterine cavity environment is more suitable for blastocysts. 3.Patients with repeated transfer failures, reducing the possibility of failure due to embryo quality. 4.People who are afraid of ectopic pregnancy, reduce the incidence of ectopic pregnancy.