The article points out that obstetricians believe that approximately 70% of postpartum hemorrhage is caused by uterine atony, which is the failure of the uterus to retract after delivery[1][2]. However, the authors draw attention to an important methodological limitation – uterine tone was accurately measured in only a small number of women out of a total sample of approximately 800 million women included in scientific studies. This fact means that a direct relationship between the tone of the uterus and the amount of blood lost during postpartum hemorrhage is not clearly demonstrated. The article emphasizes the need for caution when interpreting data on the causes of postpartum hemorrhage, as accurate measurements of uterine tone are lacking in the vast majority of investigated cases. The authors draw attention to the gaps in current scientific knowledge about the mechanisms of postpartum bleeding and to the need for further research with more accurate measurement methods.