Bleeding of more than 500mL within 24 hours after delivery of the fetus is called postpartum hemorrhage, and 80% occurs within 2 hours after delivery. Late postpartum hemorrhage refers to massive uterine bleeding that occurs during the puerperium after 24 hours of delivery, mostly seen 1 to 2 weeks after delivery. Postpartum hemorrhage is a serious complication during labor and delivery, and is one of the four major causes of maternal death. In recent years, postpartum hemorrhage has been the first cause of maternal death in China, especially in remote and backward areas. The incidence of postpartum hemorrhage accounts for 2% to 3% of all deliveries, and the actual incidence is higher due to the greater subjective factor of measuring and collecting the amount of bleeding. The causes of postpartum hemorrhage are, in order, weak uterine contractions, soft birth canal lacerations, placental factors and coagulation disorders. The four major causes can exist together or can be causal to each other. 1.Lack of contraction is the most common cause of postpartum hemorrhage, accounting for 70%. The anatomical distribution of uterine muscle fibers is inner ring, outer longitudinal and middle intertwined. Under normal circumstances, after the delivery of the fetus, the contraction of the uterine muscle fibers traveling in different directions plays an effective role in compressing the blood vessels between the muscle bundles. In case of weak contraction of uterine fibers, the effective compression of blood vessels is lost and postpartum hemorrhage occurs. The common factors are: ① Systemic factors: the woman is extremely nervous because of excessive fear of childbirth, especially lack of confidence in vaginal delivery can cause uncoordinated contractions or weak contractions. This situation may require the use of sedatives and anesthetics after delivery, which will increase the postpartum contraction weakness and cause postpartum hemorrhage; ② Obstetric factors: prolonged labor causes maternal extreme fatigue and systemic failure, or too fast labor can cause uterine contraction weakness; excessive amniotic fluid, huge children and multiple pregnancies cause uterine muscle fibers to overstretch, and the postpartum muscle fibers are poorly retracted, and the uterine muscle fibers are damaged due to multiple deliveries. All of these can cause weak contraction of the uterus. Pre-eclampsia (severe), severe anemia, uterine infections and other obstetric complications and comorbidities cause uterine muscle fiber edema and cause uterine contraction weakness; ③ uterine factors: uterine muscle fiber dysplasia, such as uterine malformation or uterine fibroids, etc. 2, placental factors account for about 20% of the causes of postpartum hemorrhage. According to the placental abruption, placenta retention, placenta adhesion and partial placenta and/or fetal membrane residue can affect contraction and cause postpartum bleeding. Retained placenta: If the placenta is not expelled 30 minutes after delivery, it is called retained placenta. It may be caused by improper use of contraction agents or rough massage of the uterus, which may stimulate spasmodic contractions and form a contraction ring at the junction of the upper and lower uterine segments or at the external cervical opening, which may cause the placenta to be retained in the uterine cavity; weak contractions or pressure on the lower uterine segment due to filling of the bladder may also cause the placenta to be retained in the uterine cavity even though it has been stripped. If the retained placenta prevents normal contractions, it will cause postpartum hemorrhage, and blood clots will gather in the uterine cavity, which will cause the cavity to increase and the contractions to be weak, and if not treated in time, it will form a vicious circle and lead to serious consequences; the causes of placental adhesions are mainly related to improper operation. If the fetus is delivered too early or too heavy massage the uterus, interfering with the normal contraction and contraction of the uterus, resulting in partial detachment of the placenta and excessive bleeding due to the opening of the blood sinus on the detachment surface; also due to the previous multiple scraping or uterine cavity operation, so that the endometrial damage can easily cause placental adhesions or implantation. Soft birth canal laceration Soft birth canal laceration includes perineal, vaginal and cervical and lower uterine laceration. Common factors: poor elasticity of vulvar tissues, inflammatory changes in vulva and vagina; emergency delivery, excessive force of labor, huge baby; vaginal surgery to assist delivery; incomplete inspection of soft birth canal, missing bleeding points. Incomplete suturing and hemostasis, etc. 4, coagulation dysfunction Common causes include placental abruption, amniotic fluid embolism, stillbirth and coagulation dysfunction caused by acute fatty liver during pregnancy, etc. A few are caused by primary blood diseases such as thrombocytopenia, leukemia, aplastic anemia or severe viral hepatitis. 5.Uterine inversion is rare, mostly caused by improper handling of the third stage of labor, such as forceful compression of the uterine fundus or violent traction of the umbilical cord.