Denne risikovurdering varierer imidlertid med progestagentypen.
Epidemiological studies have shown that the incidence of venous thromboembolism (VTE) in women with no other risk factors for VTE who use low dose oestrogen (< 50 micrograms ethinyl estradiol) combined contraceptives ranges from about 20 to 40 cases per 100,000 women-years, but this risk estimate varies according to the type of progestagen.