The success rate of embryo transfer mainly depends on the quality of embryos. The success rate of cleavage stage embryos is lower than that of blastocyst stage embryos, so most of them will choose to transfer 2 cleavage stage embryos and choose single blastocyst transfer. There are more factors affecting the success rate of embryo transfer, and the specific needs to be comprehensively analyzed according to the individual’s situation. The success of embryo transfer mainly depends on the quality of the embryos, generally speaking, the success rate of cleavage stage embryos is lower than blastocyst stage embryos, so most people will choose to transfer 2 cleavage stage embryos and choose single blastocyst transfer. Some studies have shown that single blastocyst transfer is preferred in the following cases: patients who have no obvious factors affecting pregnancy in the 1st transfer, those whose uterine factors are not suitable for twin pregnancy, such as scarred uterus, uterine deformity or after orthopedic surgery, cervical insufficiency or previous twin pregnancy or miscarriage, premature labor, etc.; those who have poor pregnancy and delivery histories; and those whose systemic conditions are not suitable for twin pregnancy. The chances of successful transfer are affected by too many factors, not just the number of embryos, so whether it is more appropriate for women to transfer one or two embryos needs to be analyzed according to their own situation.