The hemostasis of menstruation has not been extensively studied particularly since the development of laboratory tests for von Willebrand factor, a glycoprotein that plays a critical role platelet aggregation.Objective: To determine the relationship of menstrual flow to clinical and hematological parameters.Methods: We studied 155 (56 blood type O/99 blood type non-O) normal female volunteers that met the following criteria: age 12-50; not taking an oral contraceptive, estrogen, or Coumadin; not pregnant; regular periods. A questionnaire was administered regarding the patient's medical history. A pictorial chart score of menstrual blood flow was obtained using standard tampons/pads for all participants; this semi-objective measure has previously been validated to be diagnostic of menorrhagia at a score of >185. Menstrual coagulation sampling was within the first 3 days of the cycle. We then analyzed by multiple linear regression analysis the pictorial chart score assuming a log-normal distribution as a dependent variable with the following clinical and laboratory parameters as independent variables.Results: The mean age was 35.7 +/- 7.4 years. The mean pictorial chart score was 119.1 +/- 76.3.Conclusion: A history of prior births and laboratory evidence of a low von Willebrand factor antigen appear to predict for increased menstrual flow; studies are ongoing in applying these parameters in women presenting with menorrhagia.