Risk factors for severe postpartum hemorrhage: a case-control study Introduction: Postpartum hemorrhage (PPH) is an obstetric emergency. It is one of the top five causes of maternal mortality in both resource-abundant and resource-limited countries. PPH occurs in approximately 1% to 3% of all deliveries and is the leading cause of obstetric morbidity and mortality worldwide, accounting for approximately 8% of maternal deaths in developing countries and 20% of maternal deaths in developed countries. The United States has one of the highest maternal mortality rates at 11% and continues to rise, increasing from 8 to 40 cases per 10,000 deliveries. In Europe, PPH occurs in approximately 13% of deliveries. Uterine atony, the primary cause of PPH, accounts for 70% to 80% of all hemorrhages.Traditionally, PPH is defined as more than 500 mL of estimated blood loss in a vaginal delivery or more than 1000 mL of estimated blood loss during Cesarean delivery. These parameters were redefined in 2017 by the American College of Obstetrics and Gynecology as a cumulative blood loss of more than 1000 mL with signs and symptoms of hypovolemia within 24 hours of the birth process, regardless of the mode of delivery. A loss of an approximate total blood volume of more than 1500 mL will typically cause clinical features of hypovolemia. Materials and methods: The study was conducted using a retrospective, case-control research design. The study population consisted of women who gave birth between January 1 and August 1, 2024 at the Department of Obstetrics and Gynecology at the National Center for Maternal and Child Health and were diagnosed with hemorrhage. The study participants were divided into 2 groups according to the amount of blood loss in the early postpartum period: the control group was less than 1500 ml (n=72), and the case group was women with blood loss of 1500 ml or more (n=26). Research data were collected through a questionnaire with 60 questions in 3 groups pre-designed from medical history. Statistical analysis was performed using IBM SPSS 26 software. Results: The study included 98 women, maternal age was 17-44 which average 30.2±6.7 years. There were no significant differences in age, marital status, mode of delivery, and drug dosage in the case-control group. The risk of major bleeding in the early postpartum period was associated with Preeclampsia, 1.9 (OR: 1.99; 0.71-5.57), cardiovascular disease 11.2 (OR=11.2; 1.1-18.5), placenta accrete spectrum 6.5 (OR=6.5; 2.01- 21.1), increasing anemia during pregnancy 8.05 (OR=8.5; 1.08-12.5). Also, pregnancy with twins and the weight of the fetus increased the amount of postpartum hemorrhage. Also, the amount of blood lost in mothers with other births was positively correlated with the duration of labor (r=0.348). There is a risk of increased bleeding in case of co-occurring causes of bleeding (p=0.042). Conclusions: The risk of major bleeding in the early postpartum period was associated with Preeclampsia, cardiovascular disease, placenta accrete spectrum, increasing anemia during pregnancy. Also, pregnancy with twins and the weight of the fetus increased the amount of postpartum hemorrhage. Also, the amount of blood lost in mothers with other births was positively correlated with the duration of labor. There is a risk of increased bleeding in case of co-occurring causes of bleeding.