154 Chapter 7 Primary outcomes We found no increased incidence of migraine attacks in the ovulatory window in any of the three statistical models. The mixed model yielded an OR of 0·95 for migraine attacks in the ovulatory window compared to all other cycle days (95% CI: 0·88-1·02, p= 0·13) (Table 2). Table 2. Results of the mixed logistic regression model with the first day of a migraine attack as the dependent variable and the ovulatory window and perimenstrual window as fixed effects. Data from 2522 menstrual cycles from 554 patients with migraine are shown. Women (n) Migraine attacks (n) Crude OR (95% CI) Adjusted ORa (95% CI) Outside ovulatory & menstrual window 554 3941 1.00 (ref) 1.00 (ref) Ovulatory window 554 1102 0.95 (0.88 – 1.01) 0.95 (0.88 – 1.02) Menstrual window 554 1626 1.46 (1.38 – 1.56)*** 1.47 (1.38 – 1.56)*** a Adjusted ORs account for within-subject variability by including the participant as random effect. OR = odds ratio; CI = confidence interval; levels of significance = *≤0.05, **≤0.005, ***≤0.001 The case-crossover model showed an OR of 0·86 (95% CI: 0·80-0·92, p<0·001), indicating that the ovulatory window occurred less frequently just before a migraine attack compared to all other days of the menstrual cycle. When days within the perimenstrual window were removed from the analysis to investigate the effect of ovulation compared to non-perimenstrual days, the case-crossover model resulted in an OR of 0·95 (95% CI: 0·88-1·02, p=0·13) (Table 3). Table 3. Results of a case-crossover analysis comparing the odds of a migraine attack on the first day within the ovulatory window versus outside of it. The first analysis includes all control days, while the second excludes control days in the perimenstrual window. Data from 2522 menstrual cycles from 554 patients with migraine are shown. Women (n) Migraine attacks (n) Crude OR (95% CI) Control days outside ovulatory window 554 5567 1.00 (ref) Ovulatory window 554 1102 0.86 (0.80 – 0.92) Control days outside ovulatory & menstrual window 554 3941 1.00 (ref) Ovulatory window 554 1102 0.95 (0.88 – 1.02) OR = odds ratio; CI = confidence interval; levels of significance = *≤0.05, **≤0.005, ***≤0.001
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