 We propose a prospective cohort study to assess the effect of the progesterone only contraceptive pill minipill on coagulation parameters known to be associated with risk of thrombosis blood clots in women who are at increased risk for forming blood clots. We plan to recruit women with a history of venous thromboembolism VTE, blood clot in a vein and women with a history of blood tests which demonstrate an increased risk of thrombosis who desire contraception. 