Med J Aust. 1976 May 22;1(21):788, 790-3.
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.
回顾性研究的证据表明，血栓形成的风险与口服避孕药中的雌激素剂量有关。如果在大型外科手术前使用含雌激素的口服避孕药，术后发生血栓的可能性会增加四倍。吸烟的老年女性风险更高，尤其是在冬季进行手术时。建议在择期大型外科手术前六周采用屏障避孕方法（避孕套或阴道隔膜），或者在此期间使用仅含孕激素的避孕药来替代复方或序贯口服避孕药。
