ORs of developing RA overall and ACPA-positive/ACPA-negative RA according to oral contraceptive use. EIRA, Sweden, 1996–2014
| ACPA status | Oral contraceptive use* | Ca/Co | OR (95% CI)† | OR (95% CI)‡ |
| RA overall | Ever | 1717/2862 | 0.87 (0.78 to 0.97) | 0.87 (0.78 to 0.98) |
| Current | 195/331 | 0.85 (0.68 to 1.06) | 0.89 (0.71 to 1.12) | |
| Past | 1522/2531 | 0.87 (0.78 to 0.98) | 0.87 (0.78 to 0.98) | |
| Never | 861/1267 | 1.0 | 1.0 | |
| Missing | 59/115 | – | – | |
| ACPA-positive | Ever | 1135/2862 | 0.84 (0.74 to 0.95) | 0.84 (0.74 to 0.96) |
| Current | 134/331 | 0.86 (0.67 to 1.11) | 0.92 (0.71 to 1.19) | |
| Past | 1001/2531 | 0.84 (0.74 to 0.95) | 0.83 (0.73 to 0.95) | |
| Never | 572/1267 | 1.0 | 1.0 | |
| Missing | 46/115 | – | – | |
| ACPA-negative | Ever | 582/2862 | 0.94 (0.80 to 1.10) | 0.93 (0.79 to 1.10) |
| Current | 61/331 | 0.83 (0.59 to 1.17) | 0.81 (0.57 to 1.16) | |
| Past | 521/2531 | 0.95 (0.80 to 1.12) | 0.94 (0.79 to 1.11) | |
| Never | 289/1267 | 1.0 | 1.0 | |
| Missing | 13/115 | – | – |
↵*Participants who started OC use during index-year (four cases/seven controls) were excluded from the analysis. Ever is the sum of current and past OC users.
↵†Adjusted for age and residential area.
↵‡Adjusted for age, residential area, smoking (pack-years) and alcohol consumption (low (including non-drinkers), medium and high).
ACPA, anticitrullinated protein antibodies; Ca/Co, number of cases/controls; EIRA, Epidemiological Investigation of Rheumatoid Arthritis; OC, oral contraceptive; RA, rheumatoid arthritis.