In natural pregnancy, the embryo is developed to the blastocyst stage before entering the uterine cavity. Therefore, in the in vitro fertilization and embryo transfer techniques, blastocyst stage embryo culture and transfer are more in line with the natural pregnancy physiology. Characteristics of blastocyst stage embryo culture and transfer: 1. Blastocyst stage embryo culture and transfer are more consistent with the physiology of pregnancy. 2. Blastocyst stage embryo culture allows for embryo selection, and those embryos that can develop to the blastocyst stage are likely to be the best quality embryos. 3. Blastocyst stage embryo culture and transfer technique can reduce the incidence of multiple births and can increase the clinical pregnancy rate by about 20%. The indications for blastocyst culture and transfer include: 1. The number of embryos available for transfer is 4 or more. 2. Delayed embryo transfer due to fluid in the uterine cavity or other reasons. 3. There has been unexplained failure of in vitro fertilization and embryo transfer. 4. There are multiple discarded embryos to be discarded