Risk of acute cerebrovascular events related to low oestrogen oral contraceptive treatment

To establish if an association exists between use of oral contraceptives (OC) and the occurrence of cerebral arterial thromboembolism, cerebral venous thrombosis and retinal vein/artery thrombosis, we identified all women aged 15-44 years resident in the province of Parma, Italy, who were hospitalized because of a documented cerebral or retinal thromboembolic event during the period 1989-1993. The numbers of users and nonusers of OC were estimated from drug sale data and demographic statistics for the province. There were 21 cases of cerebral arterial thromboembolism during the study period: 10 in OC users and 11 in nonusers, for an estimated incidence rate of 1.70 and 0.35 per 10,000 woman-years OC of use and nonuse, respectively (RR=4.8, 95% CI = 1.8-9.0). Eight cases of cerebral venous thrombosis were observed: 6 in OC users and 2 in nonusers (both in puerperium), for an incidence rate of 1.00 and 0.06 per 10,000 woman-years, respectively (RR=16.7, 95% CI = 3.3-81.4). Finally, 13 cases of retinal vein/artery thrombosis were found: 1 in OC users and 12 in nonusers, for an incidence rate of 0.17 and 0.37 per 10,000 woman-years, respectively (RR=0.46, 95% CI = 0.06-3.7). In our population study the use of low oestrogen OC was associated with an increased risk of cerebral venous thrombosis and ischemic stroke, but not of retinal vein/artery thrombosis.