Postpartum hemorrhage usually occurs within 24 hours after delivery, and is more common within two hours after delivery, occurring for the following reasons: 1, postpartum contraction weakness, such as a long labor, fatigue in the middle of labor, prone to postpartum uterine non-contraction, contraction weakness; 2, placental factors, multiple abortions, pregnancy, the placenta can not deliver itself, prone to placenta-induced postpartum hemorrhage; 3, soft The tear of the birth canal damage, the tear of the birth canal may occur in huge babies, leading to postpartum hemorrhage; 4, coagulation dysfunction; 5, pregnant women with multiple pregnancies and deliveries, the risk of postpartum hemorrhage will increase, because it may lead to weak contractions after delivery.