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.