Black C, Kaye JA, Jick H. Clinical risk factors for venous thromboembolus in users of the combined oral contraceptive pill. Br J Clin Pharmacol. 2002 Jun;53(6):637-40.

AIMS:To estimate the risk of venous thromboembolism among women prescribed the oral contraceptive pill who have acute clinical conditions such as lower limb fractures, compared with women with idiopathic venousthromboembolism.

METHODS:A nested case-control analysis using the General Practice Research Database, January 1993 to December 1999 was carried out. The participants were women aged 15-39 years, prescribed third generation oral contraceptives (gestodene and desogestrel) or oral contraceptives containing levonorgestrel. The main outcome measures were odds ratios as a measure of the relative risk estimate for venous thromboembolism in women withclinical conditions that predispose to VTE.

RESULTS:The adjusted relative risk estimate for venous thromboembolism among patients with the acute clinicalconditions, compared with those without such illness, and adjusted for oral contraceptive use, was 17 (95% CI 6.5, 46).

CONCLUSIONS:This paper documents the strong independent association between certain acute clinicalconditions and venous thromboembolism in women prescribed oral contraceptives. Failure to accurately identify and exclude such patients from a study of the effect of oral contraceptives on the risk of venous thromboembolismwould result in an underestimate of the risk of venous thromboembolism associated with oral contraceptives.

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