The results showed that women who are obese (a body mass index of 30 or more) and use oral contraceptives are 30 times more prone to cerebral venous thrombosis (CVT), compared to women with normal weight.
CVT, or clot of cerebral veins, is an uncommon disorder in the general population. However, it has a higher frequency among patients younger than 40 years of age and women who are pregnant or receiving hormonal contraceptive therapy.
However, the study found no association between obesity and CVT among men or women who did not use oral contraceptives.
"The increased risk of CVT associated with oral contraceptives in the presence of obesity might make physicians reluctant to prescribe oral contraceptives to obese women, said Jonathan M. Coutinho from the University of Amsterdam in Netherlands.
Risk factors for CVT overlap some with those for venous thromboembolism (VTE) and include cancer and oral contraceptives but there also are risk factors specific to CVT including infections and head trauma.
"Use of oral contraceptives has also been associated with increased risk of arterial ischemic stroke in obese women," commented Chirantan Banerjee from the University of South Carolina.
Withholding oral contraceptives may lead to an increase in unintended pregnancies and thus the number of pregnancy-related blood clot cases, the researchers pointed out in the study published online by JAMA Neurology.
Educating and informing obese women of the increased risk would be prudent, as would be consideration of alternate non-hormonal oral contraceptives options.
"Alternative methods of contraception that are not associated with blood clots, such as intrauterine device, might be offered to these women," the researchers suggested.
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