Observations on the clotting of menstrual blood and clot formation

Pathomorphologic and biochemical data on clots at menstruation reveal that these clots are not composed of fibrin. They are not related to coagulation but are red cell aggregations to mucoid substances, mucoproteins, and/or glycogen. Present evidence indicates that they form in the vagina. Coagulation factors are decreased in menstrual discharge, and fibrinogen is absent. Menstrual discharge contains, besides plasminogen activator, decreased amounts of plasminogen and plasmin inhibitor. Alpha-1-trypsin inhibitor and alpha-2-macroglobulin levels, determined by immunoassays, are ⅔ of that found in peripheral blood. Fibrinolysis breakdown products demonstrated in menstrual discharge had the biochemical characteristics of fibrinogen breakdown products rather than those from fibrin. The functional consequences of these observations are evaluated. A striking difference between the amounts of plasminogen and plasmin inhibitor sampled from the cavity of the uterus and the vagina provide evidence for cervical mucus as an active proteolytic system.