In vitro twins are reduced at 8-11 weeks of pregnancy, and the shorter the pregnancy, the higher the success rate of reduction. If a pregnant woman is of advanced maternal age, has a history of spontaneous miscarriage, or has delivered a fetus with congenital disease, it is recommended to consider reducing the fetus after the middle of pregnancy, and the fetus can be retained in the middle of pregnancy on the basis of merit. If the fetus or the mother cannot tolerate it, it is recommended that the better developed fetus be retained. The chance of having twin pregnancies through IVF is relatively high. The reduction of fetus should be determined according to the basic condition of the pregnant woman.