As the incidence of infertility increases, access to assisted conception and the use of ovulation-promoting drugs increases, thus leading to a higher incidence of multiple pregnancies. The number of embryos to be retained is determined by the uterine condition, monozygotic twins, size, and the presence of serious complications. Although our reduction technology has reached a very advanced level, both early and late reduction cannot completely avoid complications such as miscarriage and infection, so the doctor will inform the patient and the family about the relevant matters before the operation, including the choice of the timing of reduction, which is one of the most important aspects, and this choice is a very serious challenge for both the family and the patient. The timing of reduction is divided into early reduction and middle and late reduction. In our hospital, early reduction is generally recommended, but late reduction is recommended in the following cases: 1. Advanced age, because of the increased incidence of spontaneous abortion and fetal malformation, the embryo faces increased chances of natural selection and artificial selection, if the embryo is spontaneously aborted is the best ending, avoiding the risk of reduction as well as the cost and pain; if all embryos This is one of the important reasons for reduction of fetus at advanced age and later in life. 2. Patients with a history of repeated spontaneous abortions, because the possibility of embryos stopping development naturally is high. 3, Couples with genetic diseases or chromosomal abnormalities in both or one of them, which clearly require prenatal diagnosis, should choose late reduction. 4.Patients with preterm miscarriage, the possibility of early reduction leading to all miscarriage is high and the possibility of infection increases, so it is recommended to choose late reduction.