Cyclical changes in coagulation factors associated with the use of progestational agents

The activity of factors II, VII, VIII, IX, X and fibrinogen and factor VIII antigen levels were followed during a single menstrual cycle in three females using oral contraceptive agents, and in two controls. Marked cyclical variation occurred in the activity of factor VII and VIII, but not in factor VIII antigen levels. Less marked changes occurred in factor II and fibrinogen.