Tranexamic Acid for the Prevention of Postpartum Hemorrhage in Pregnant Women With Placenta Previa

Inclusion Criteria: * Age of 18 years or older * Diagnosed with Placenta previa before cesarean delivery by ultrasound（Placenta previa defined by a placental edge below 20mm from internal cervical os diagnosed at the most recent transvaginal ultrasound examination before delivery） * Gestational age ≥ 34 weeks * Available venous hematocrit value in the week before the cesarean * Prenatal hemoglobin level in the week before the cesarean \> 90 g/l * Undergoing cesarean delivery * Signed informed consent Exclusion Criteria: * Known hypersensitivity to tranexamic acid or concentrated hydrochloric acid * History of venous (deep vein thrombosis and/or pulmonary embolism) or arterial thrombosis (angina pectoris, myocardial infarction, or stroke) * History of epilepsy or seizure * Any known active cancer, active cardiovascular, renal, or liver disorders * Autoimmune diseases such as lupus, rheumatoid arthritis, Sjogren's disease, and inflammatory bowel disease * Sickle cell disease * Severe hemorrhagic disease * Administration of low-molecular-weight heparin or antiplatelet agents within one week prior to delivery * Severe coagulation disorders with prothrombin time or activated partial thromboplastin time exceeding the upper limit of normal, or platelet count less than 80×109/L * placenta abruption * In-utero fetal death * Eclampsia or HELLP syndrome * Acquired color vision deficiency or subarachnoid hemorrhage * Severe bleeding with estimated blood loss exceeding 500 ml, within 12 hours before cesarean delivery * Known congenital or acquired thrombophilias, including antiphospholipid antibody syndrome * Participation in another intervention study where the primary outcome includes postpartum bleeding or thromboembolism or the study intervention potentially affects postpartum bleeding or thromboembolism