Thrombosis-perspective on a major side effect of oral contraceptives.

Evidence from retrospective studies suggests that the risk of thrombosis is related to the dose of oestrogen in oral contraceptives. Postoperative thrombosis is four times more likely to occur if oral contraceptives containing oestrogen are used before a major surgical procedure. Older women who smoke are at greater risk, especially when the surgery is performed during the winter months. It is recommended that barrier methods of contraception (condom or vaginal diaphragm) be employed during the six weeks before an elective major surgical procedure or that a progestogen-only pill be used in place of a combined or sequential oral contraceptive for this period of time.