Embryo culture usually takes 5 to 7 days. Embryo culture simulates normal fertilization and embryo development in vitro. On the third day of embryo culture, the embryo is called cleavage stage embryo, or fresh embryo, in order to improve the success rate of transplantation, the fresh embryo can continue to be cultured in vitro until day 5-7, the embryo grows into a cell mass with blastocyst cavity, and at this time, the embryo is called late blastocyst. The earlier the blastocyst is formed, the better the quality of the embryo and the higher the chance of success after transfer. During the process of embryo culture, the quality of the embryo can be assessed based on three dimensions: the speed of embryo development, the inner cell mass, and the outer trophoblast cells, and the blastocyst can be graded. There is a possibility of unhealthy embryos and embryo death during embryo culture. Embryo culture is the key to determining the success of IVF.