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Oral contraceptives are a risk factor for cerebral vein thrombosis.

In the study by Martinelli and colleagues concerning the association between factor V Leiden mutation and cerebral vein thrombosis use of oral contraceptives was the most frequent circumstantial risk factor present at the time of the episode yet relative risk for oral contraceptives was underestimated to be 2.1 and was not statistically significant. However pregnant women and those in the postpartum period should not have been included in the statistical analysis because pregnancy and use of oral contraceptives are mutually exclusive. Re-analysis of the data excluding 1 pregnant and 3 postpartum women and their matched controls showed that: 75% (12/16) of patients with cerebral vein thrombosis used oral contraceptives; 42% (20/48) of controls used oral contraceptives; and 3) the odds ratio was 4.2 (95% confidence interval: 1.2-14.9 p = 0.04). The odds ratio did not change with an adjustment for age. This magnitude of relative risk is similar to that found by Vandenbroucke and colleagues for deep vein thrombosis in the lower limbs. This study also looked at the synergy between the Leiden V mutation and oral contraceptives; oral contraceptive users who carried the mutation had a greater than 30-fold risk of thrombosis in comparison to non-carriers. Martinelli and colleagues have too small a sample to make such determinations with regard to cerebral vein thrombosis.