Case-referent evaluations of data on reproduction and breast feeding in women (179 cases of RA and 259 referents) from southeastern Sweden, 1980–95, with adjustment for age
| Exposed cases/referents | OR4-150 | 95% CI4-150 95% | |
| Menarche | |||
| Early | 20/28 | 1.1 | 0.6 to 2.1 |
| Normal4-151 | 109/163 | 1.0 | Reference |
| Late | 35/33 | 1.6 | 1.0 to 2.8 |
| Menopause | |||
| Early | 15/13 | 1.6 | 0.7 to 3.7 |
| Normal4-152 | 48/63 | 1.0 | Reference |
| Late | 20/15 | 1.6 | 0.7 to 3.4 |
| Fertile period | |||
| Short | 23/13 | 2.5 | 1.1 to 5.4 |
| Normal4-153 | 43/60 | 1.0 | Reference |
| Long | 13/10 | 1.5 | 0.6 to 3.9 |
| Current OC4-150use4-155 | 7/31 | 0.3 | 0.1 to 0.8 |
| Other exogenous sex hormones4-154 | 7/16 | 0.5 | 0.2 to 1.2 |
| Never parous | 32/31 | 1.0 | Reference |
| Ever parous4-160 | 145/221 | 0.5 | 0.3 to 0.9 |
| First child at age (years)4-160 | |||
| ⩽19 | 18/19 | 1.8 | 0.9 to 3.6 |
| 20–29 | 106/180 | 1.0 | Reference |
| ⩾30 | 21/22 | 1.4 | 0.7 to 2.7 |
| Breast feeding4-164 | |||
| Never4-161 | 22/16 | 1.0 | Reference |
| Ever | 123/205 | 0.4 | 0.2 to 0.8 |
| Duration (months) | |||
| <5 | 26/28 | 0.4 | 0.1 to 1.1 |
| 5–14 | 66/108 | 0.4 | 0.2 to 0.9 |
| 15–24 | 19/51 | 0.3 | 0.1 to 0.7 |
| ⩾25 | 12/18 | 0.4 | 0.1 to 1.3 |
| p for trend = 0.063 | |||
↵4-150 OC = oral contraceptive; OR = Mantel-Haenszel odds ratio; CI = confidence interval as outlined by Robins et al.36
↵4-151 Menarche at age 13–15.
↵4-152 Menopause at age 48–53.
↵4-153 Fertile period of 34–40 years.
↵4-155 At time of diagnosis of RA.
↵4-154 Before onset of RA symptoms.
↵4-160 Adjustment also for marital status.
↵4-164 Adjustment also for marital status and socioeconomic status.
↵4-161 Parous women having never breast fed.