Prevalence of migraine on each day of the natural menstrual cycle.

Diary data from 155 women were analyzed using within-woman analysis. Compared with all other times of the cycle, migraine was 1.7 times more likely to occur during the 2 days before menstruation and 2.1 times more likely to be severe and 2.5 times more likely to occur during the first 3 days of menstruation and 3.4 times more likely to be severe. This confirms that migraine at menstruation is different from nonmenstrual attacks, even within individuals.