However, multiple pregnancies (two or more fetuses in a single pregnancy) are pathological pregnancies that often present multiple complications during pregnancy and delivery, posing a serious threat to the safety of the mother and child. The perinatal mortality rate also increases significantly with the number of fetuses, and even if multiple preterm infants survive, their physical and intellectual quality may decline. In order to effectively and safely control the number of embryos and deliveries, to reduce the damage to the mother and child from multiple pregnancies, and to improve the survival rate and quality of surviving children, it is necessary to perform elective reduction of multiple pregnancies. The disadvantages of multiple pregnancies outweigh the benefits. Therefore, reduction of fetus is to protect the life rights of mother and child and to ensure the quality of fetal life. The Ministry of Health’s Technical Guidelines for Assisted Human Reproduction clearly stipulates the number of embryos to be transferred, and the chance of multiple pregnancies occurring with assisted conception has greatly exceeded the incidence of multiple pregnancies in natural pregnancies. Therefore, the Ministry of Health also clearly stipulates that multiple pregnancies must be reduced, avoiding twin pregnancies and strictly prohibiting the delivery of three or more pregnancies. The complications for pregnant women with multiple pregnancies: 1. Miscarriage: The rate of spontaneous miscarriage in twin pregnancies is 2 to 3 times that of singleton pregnancies. The greater the number of fetuses, the greater the risk of miscarriage, associated with embryonic malformations, abnormal placental development, impaired placental circulation and relative narrowing of the uterine cavity volume. The incidence of gestational hypertension syndrome is three times higher than that of singleton pregnancies, and the symptoms appear early and are mostly severe, often not easily controlled. Eclampsia is a serious threat to the health of mother and child. 3, anemia: the incidence is 2.4 times higher than that of singleton pregnancies. Due to the increase in blood volume and the need for iron, iron deficiency anemia is common in the second half of pregnancy. If folic acid deficiency can lead to megaloblastic anemia. Anemia leads to fetal hypoxia, which further promotes intrauterine growth retardation. 4, excessive amniotic fluid: the incidence of excessive amniotic fluid in twin pregnancies is 12%, and is associated with twin fetal transfusion syndrome and fetal malformations. 5, placenta abruptio and placenta praevia: placenta abruptio is the main cause of prenatal hemorrhage in twin pregnancies. It starts rapidly, develops quickly and poses a serious threat to the health of mother and child. Due to the large area of the placenta, it is easy to extend to the lower part of the uterus and cover the endocervix, forming placenta praevia, the incidence is 1 times higher than that of singleton. 6, intrahepatic cholestasis during pregnancy: 2 times higher than that of singleton. It is easy to cause preterm labor, fetal distress, stillbirth and stillbirth. 7, postpartum hemorrhage and puerperal infection: uterine muscle fiber overstretching leads to weak contraction of the uterus, large placental attachment surface, easy to develop postpartum hemorrhage and increase the chance of infection. The effects of multiple births on the fetus The perinatal mortality rate is significantly higher in multiple births. 1, preterm birth: 50% of the complications of preterm birth. The incidence of preterm labor is high due to high intrauterine pressure when there are many fetuses and excessive amniotic fluid. Most of the preterm births occur naturally or after premature rupture of fetal membranes. According to statistics, the average gestation period of twin pregnancies is only 37 weeks. The fetal growth retardation in utero is the most common complication of multiple pregnancies. The incidence is 12% to 34%, and its degree increases with the gestational weeks, and the uncoordinated growth between the two fetuses is more significant in monozygotic twins than in dizygotic twins. 3, intrauterine death of one of the twins: In multiple pregnancies, not only are there more miscarriages and premature births than in singleton pregnancies, but there are also more intrauterine deaths. Sometimes, one of the twins dies in utero and the other fetus continues to grow and develop. Fetal death in late pregnancy can cause diffuse intravascular coagulation. About 30% of coagulation dysfunction occurs after 4 weeks of retention. 4, fetal malformation: twin pregnancy fetal malformation rate is 2 times higher than that of singleton, the reason for the increased malformation rate is not clear, intrauterine compression can cause malformed feet, congenital hip dislocation and other fetal local malformations.