HDCN Article Review/Hyperlink

WHO Collaborative Study of Cardiovascular Disease and Steroid Hormone Contraception

Overall stroke risk and combined oral contraceptives: results of an international, multicentre, case-control study

Lancet (Aug) 348:498-510 1996

The risk of stroke associated with oral contraceptives (OCs) is not clearly known. Such a risk was identified about 25 years ago, but the doses of estrogen and progestogens in OCs are now much lower than at the time those studies were performed. In two back to back studies in Lancet, risk of both ischemic and hemorrhagic stroke was assessed in a case controlled study based on centers in Europe, Africa, and Asia.

Ischemic stroke: The odds ratio was increased to 3.0 in women taking OCs. The ratio was higher in women with preexisting hypertension or those who smoked, although in the abstract, the risks from hypertension or smoking and OCs are considered together, rather than separately. There appeared to be a lower risk of stroke with low dose preparations in the women from Europe, but not in women from developing countries.

Hemorrhagic stroke: The risk of hemorrhagic stroke was not increased in women taking OCs from Europe (odds ratio 1.4, confidence interval not greater than 1.0), but was increased slightly in women from developing countries. Overall, the authors estimated that about 8-13% of all cases of stroke in women aged 20-44 in Europe and developing countries can be attributed to OC use.

Comment: I don't like how the data are reported in the abstract, where the odds ratios of hypertension and cigarette smoking are reported in combination with OC use. When the probability of an event is low, the odds ratio is not really a good indicator of risk; e.g., if the risk is 1/100,000, doubling it does not really mean very much. The shortcomings of the odds ratio re data interpretation can be found at the Bandolier site. (John T. Daugirdas, M.D., University of Illinois at Chicago)

The abstracts of these papers are available at the Lancet site. The first time you access the Lancet site, you will need to register to get a login ID and password. -- Ischemic stroke abstract-- Hemorrhagic stroke abstract.