Table 1.
Reproductive factors and risk of seizure/epilepsy (1989–2005)*
| Variable | % | Isolated seizure† | Epilepsy† | Any unprovoked seizure† | |||
|---|---|---|---|---|---|---|---|
| Age at menarche | cases | RR (95%CI)* | cases | RR (95%CI)* | cases | RR (95%CI)* | |
| <12 years | 24% | 33 | 1.76 (1.10,2.81) | 33 | 0.83 (0.55, 1.26) | 48 | 0.97 (0.68, 1.38) |
| 12–13 years | 58% | 41 | 1.00 | 89 | 1.00 | 109 | 1.00 |
| 14+ years | 18% | 21 | 1.67 (0.98,2.84) | 28 | 0.90 (0.58, 1.39) | 38 | 1.02 (0.69, 1.49) |
| Menstrual regularity at age 18‡ | |||||||
| Regular | 76% | 60 | 1.00 | 83 | 1.00 | 112 | 1.00 |
| Irregular | 24% | 19 | 0.87 (0.51,1.49) | 38 | 1.67 (1.12, 2.51) | 44 | 1.40 (0.97, 2.02) |
| Menstrual cycle length at age 18‡ | |||||||
| ≤ 25 days | 11% | 6 | 0.53 (0.23,1.26) | 17 | 1.40 (0.81,2.44) | 21 | 1.28 (0.78, 2.09) |
| 26–31 days | 66% | 55 | 1.00 | 72 | 1.00 | 94 | 1.00 |
| 32–39 days | 15% | 14 | 1.16 (0.63,2.12) | 21 | 1.34 (0.80,2.25) | 28 | 1.37 (0.88, 2.14) |
| ≥ 40 days | 8% | 8 | 1.08 (0.50,2.35) | 13 | 1.71 (0.90, 3.23) | 16 | 1.51 (0.85, 2.66) |
| Menstrual regularity during follow-up‡ | |||||||
| Regular | 90% | 50 | 1.00 | 94 | 1.00 | 119 | 1.00 |
| Irregular | 10% | 13 | 2.21 (1.16,4.20) | 8 | 0.54 (0.25,1.16) | 12 | 0.70 (0.37, 1.31) |
| Menstrual cycle length during follow-up‡ | |||||||
| ≤ 25 days | 17% | 13 | 1.40 (0.74,2.67) | 18 | 1.04 (0.60,1.81) | 23 | 1.04 (0.64, 1.68) |
| 26–31 days | 68% | 38 | 1.00 | 62 | 1.00 | 81 | 1.00 |
| 32–39 days | 10% | 7 | 1.27 (0.55,2.93) | 16 | 1.55 (0.86,2.78) | 20 | 1.51 (0.90, 2.54) |
| ≥ 40 days | 5% | 9 | 2.50 (1.16,5.40) | 6 | 0.90 (0.36,2.21) | 9 | 1.11 (0.53, 2.31) |
| Oral contraceptives | |||||||
| Never | 14% | 12 | 1.04 (0.55,1.94) | 17 | 0.87 (0.51,1.48) | 22 | 0.88 (0.55, 1.41) |
| Past | 77% | 67 | 1.00 | 105 | 1.00 | 136 | 1.00 |
| Current | 9% | 6 | 1.04 (0.43,2.47) | 15 | 1.20 (0.67,2.12) | 20 | 1.38 (0.84, 2.27) |
Multivariate models adjusted for family history of seizure or epilepsy, smoking (never, past current), hypertension, high cholesterol, type 2 diabetes mellitus, stroke, brain tumor, parous state, history of oral contraceptive use, menstrual regularity at age 18–22 (regular or not regular), age at menarche (years), body mass index (kg/m2). The missing exposure categories and the corresponding case numbers are not shown.
“Isolated seizure” includes single unprovoked seizure and acute symptomatic seizure (single seizure with systemic causes, single seizure with neurologic causes, and recurrent provoked seizure). “Epilepsy” includes symptomatic partial epilepsy, idiopathic/cryptogenic partial epilepsy or partial epilepsy of unknown cause, idiopathic generalized epilepsy, and nonclassifiable epilepsy. “Any unprovoked seizure” includes single unprovoked seizure or epilepsy.
The study period was from 1993 – 2005 for menstrual irregularity variables.