Female reproductive factors and risk of seizure or epilepsy: data from the Nurses' Health Study II.

Reproductive factors are associated with seizures in women with epilepsy. We prospectively examined the association between reproductive factors and the risk of adult-onset isolated seizure, epilepsy, or any unprovoked seizure (defined as single unprovoked seizure or epilepsy) among 114,847 Nurses' Health Study II participants followed from 1989 to 2005. Validated seizure questionnaires and medical records were used to confirm incident cases of isolated seizure (n = 95) or epilepsy (n = 151). Overall, there were no significant associations between any reproductive factor and risk of any unprovoked seizure (n = 196). However, menstrual irregularity at ages 18-22 years was specifically associated with an increased risk of epilepsy [relative risk (RR) 1.67, 95% confidence interval (CI) 1.12-2.51]. Menstrual irregularity during follow-up (RR 2.21, 95% CI 1.16-4.20) and early age at menarche (<12 years vs. 12-13 years; RR 1.76, 95% CI 1.10-2.81) increased the risk of isolated seizure. Oral contraceptive use and parity were not associated with isolated seizure or epilepsy. Therefore, menstrual factors were associated with risk of seizure and epilepsy.