The presence of two or more fetuses in the uterus at the same time in a single pregnancy is called a multiple pregnancy. In recent years, due to the widespread use of assisted reproductive technology, the incidence of multiple pregnancies has increased significantly. Some couples deliberately seek to have twins or multiples and apply ovulation-promoting drugs on their own or ask their doctors to do so. Physiologically, the human uterus is most suitable for conceiving one fetus at a time, and multiple pregnancies are high-risk pregnancies with many complications during pregnancy and delivery and high perinatal and neonatal mortality, so they should be taken seriously and should undergo fetal reduction surgery for three or more pregnancies. The main hazards of multiple pregnancies are the following: 1) Maternal complications: (1) Anemia: anemia is 2-3 times more common in twin pregnancies than in single pregnancies and is related to iron and folic acid deficiency. (2) hypertensive disorders of pregnancy: twin pregnancies can be up to 40% of the complications of hyperemesis, 3-4 times more than singleton, and the onset is early and severe. (3) Excessive amniotic fluid and premature rupture of membranes: the incidence of excessive amniotic fluid in twin pregnancies is 12%, and the incidence of premature rupture of membranes is 14%. (4) Postpartum hemorrhage: the average postpartum hemorrhage is ≥500ml in twin fetuses delivered vaginally. (5) Uterine rupture: the incidence increases significantly in patients with scarred uterus with unicornuate uterus and previous history of uterine surgery (such as cesarean section, myomectomy, etc.), which seriously threatens the health of mother and child. 2. Perinatal complications: (1) Preterm delivery: The risk of preterm delivery in twin pregnancies is about 7-10 times higher than that in singleton pregnancies, mostly due to premature rupture of membranes or high intrauterine pressure and serious maternal and infant complications. The higher the number of fetuses, the earlier the preterm birth and the lower the chance of neonatal survival. (2) Intrauterine growth restriction: fetal growth retardation, twin fetal transfusion syndrome, one fetal malformation or even death. (3) Fetal interlock and head-up collision: can cause obstructed labor and endanger the life of mother and child. (4) Fetal malformation: the incidence is twice as high as that of monozygotic twins, and some malformations are unique to monozygotic twins, such as conjoined twins and heartless malformation.