We describe the pattern of change in coagulation parameters during the course of severe postpartum hemorrhage in a retrospective cohort study among 1312 women experiencing severe postpartum hemorrhage necessitating blood transfusion. Levels of hemoglobin, hematocrit, platelet count, fibrinogen, activated partial thromboplastin time (aPTT) and prothrombin time (PT) per categorized volume of blood loss during severe postpartum hemorrhage were described and compared between women with and without the composite adverse outcome. Need for surgical intervention, severe acute maternal morbidity, and maternal mortality were jointly considered the composite adverse outcome. Of the 1312 women, 463 (35%) developed the composite adverse outcome. The incidence of a fibrinogen level < 2 g/L was 26% (342 per 1312). Low fibrinogen and prolonged aPTT during the first 2 L of hemorrhage were associated with a subsequent composite adverse outcome; median fibrinogen and aPTT among women with and without the composite end point after 1.5 to 2 L of hemorrhage were 1.5 g/L (interquartile range [IQR], 1.0-1.9) vs 2.7 g/L (IQR, 1.9-3.4) and 39 s (IQR, 30-47) vs 32 s (IQR, 28-36), respectively. PT and platelet count as assessed during the first 2 L of hemorrhage were not associated with morbidity or mortality. Our results suggest that detection of low levels of fibrinogen and elevated aPTT levels during early postpartum hemorrhage can contribute to the identification of women that may benefit from targeted hemostatic treatment. Essential in this identification process is the moment of reaching a level of fibrinogen of <2 g/L during the course of postpartum hemorrhage.