The exact pathogenesis of placenta previa is unclear, but it is related to vascular lesions, mechanical factors, sudden decrease in intrauterine pressure, and other factors. 1. Vascular lesions: pregnant women with hypertensive disorders of pregnancy, pregnancy complications such as chronic kidney disease, resulting in vascular lesions, hemorrhage of the capillaries of the fundus metamorphosus, the formation of hematoma between the placenta and the uterine wall, resulting in placental abruption. 2. Mechanical factors: the pregnant woman’s abdomen is hit by external forces, resulting in the stretching of the uterine wall or uterine contraction, so that the placenta and the uterine wall are misplaced and there is a detachment of the placenta. 3. Sudden decrease of pressure in the uterine cavity: the first child of a twin pregnancy is delivered too fast, and the amniotic fluid flows out too fast when the membranes are broken artificially, which leads to a sudden decrease of pressure in the uterine cavity, and sudden contraction of the uterus makes the placenta and the uterine wall misaligned and the placenta is peeled off. 4. Other factors: the risk of placenta abruption is also elevated in pregnant women who have had multiple births at an advanced age, have a history of placental abruption, smoke and take drugs, and have assisted reproduction. Pregnant women with symptoms such as vaginal bleeding and abdominal pain in the middle and late stages of pregnancy need to consult a doctor in time to rule out the possibility of placental abruption.