Oral contraceptives and stroke: findings in a large prospective study.

Abstract

Prospective data from the Oxford Family Planning Association contraceptive study suggest only a modest increase in the risk of subarachnoid hemorrhage among oral contraceptive (OC) users. The investigation included 17000 married women recruited to the study in 1968-74 at 25-39 years of age. By January 1984 a total of 192000 woman-years of observation were available for analysis. Data on age past hospital referral for hypertension cigarette smoking and OC use were analyzed for the 13 cases of subarachnoid hemorrhage and 31 cases of nonhemorrhagic stroke (strokes of embolic thrombotic or unknown pathogenesis) observed in the series. The risk of subarachnoid hemorrhage was strongly related to cigarette smoking and past hospital referral for hypertension but weakly related to OC use. On the other hand hypertension or smoking appeared to have little adverse effect on nonhemorrhagic stroke but current OC use emerged as a cleark risk factor regardless of duration of use. Risk of nonhemorrhagic stroke was also examined in relation to type of OC used. No strokes were observed in 9100 woman-years of observation of women using OCs containing less than 50 mcg estrogen while 13 strokes were noted in 39400 years of observation of women using OCs with a higher estrogen dose.