| RA | JIA | |||||
| Cases n = 333 | Controls n = 1332 | OR (95% CI) | Cases n = 3334 | Controls n = 13 336 | OR (95% CI) | |
| Maternal age, years | ||||||
| <25 | 120 | 482 | 1.0 (0.8 to 1.3) | 1017 | 4077 | 1.0 (0.9 to 1.1) |
| 25–29 | 129 | 519 | 1 | 1253 | 4967 | 1 |
| 30–34 | 62 | 242 | 1.0 (0.7 to 1.4) | 773 | 3118 | 1.0 (0.9 to 1.1) |
| 35+ | 22 | 89 | 1.0 (0.6 to 1.7) | 291 | 1174 | 1.0 (0.9 to 1.2) |
| Maternal civil status | ||||||
| Married | 210 | 831 | 1 | 2237 | 9088 | 1 |
| Other | 108 | 429 | 1.0 (0.7 to 1.3) | 720 | 2847 | 1.0 (0.9 to 1.1) |
| No of older siblings | ||||||
| 0 | 140 | 597 | 1 | 1457 | 5844 | 1 |
| 1–2 | 175 | 678 | 1.1 (0.9 to 1.4) | 1705 | 6717 | 1.0 (0.9 to 1.1) |
| ⩾3 | 18 | 57 | 1.4 (0.8 to 2.4) | 172 | 774 | 0.9 (0.8 to 1.1) |
| Season of birth | ||||||
| January–March | 88 | 366 | 0.9 (0.6 to 1.3) | 912 | 3532 | 1.08 (1.0 to 1.2) |
| April–June | 94 | 355 | 1 | 860 | 3598 | 1 |
| July–September | 77 | 325 | 0.9 (0.6 to 1.2) | 797 | 3229 | 1.0 (0.9 to 1.2) |
| October–December | 74 | 286 | 1.0 (0.7 to 1.4) | 765 | 2977 | 1.1 (1.0 to 1.2) |
| Mode of delivery | ||||||
| Vaginal | 302 | 1210 | 1 | 2946 | 11 930 | 1 |
| Caesarean | 31 | 122 | 1.0 (0.7 to 1.5) | 388 | 1406 | 1.1 (1.0 to 1.3) |
| Type of birth | ||||||
| Singletons | 329 | 1309 | 1 | 3268 | 13 044 | 1 |
| Multiple birth | 4 | 23 | 0.7 (0.2 to 2.0) | 65 | 288 | 0.9 (0.7 to 1.2) |
| Birth weight, g | ||||||
| <3000 | 43 | 226 | 0.7 (0.5 to 1.0) | 533 | 2181 | 1.0 (0.9 to 1.1) |
| 3000–3999 | 239 | 910 | 1 | 2237 | 8936 | 1 |
| ⩾4000 | 50 | 194 | 1.0 (0.7 to 1.4) | 553 | 2156 | 1.0 (0.9 to 1.1) |
| Birth weight for gestational age* | ||||||
| SGA | 10 | 73 | 0.5 (0.3 to 1.0) | 116 | 470 | 1.0 (0.8 to 1.2) |
| AGA | 307 | 1203 | 1 | 3061 | 12 093 | 1 |
| LGA | 10 | 25 | 1.6 (0.7 to 3.3) | 68 | 349 | 0.8 (0.6 to 1.0) |
| Gestational age, days | ||||||
| ⩽258 | 13 | 80 | 0.6 (0.7 to 1) | 137 | 667 | 0.8 (0.7 to 1.0) |
| 259–293 | 278 | 1092 | 1 | 2851 | 11 476 | 1 |
| ⩾294 | 41 | 154 | 1.1 (0.7 to 1.5) | 326 | 1115 | 1.2 (1.03 to 1.3) |
| Congenital malformation | ||||||
| No | 328 | 1298 | 1 | 3052 | 12 213 | 1 |
| Yes | 5 | 34 | 0.6 (0.2 to 1.5) | 77 | 300 | 1.0 (0.8 to 1.3) |
| Maternal smoking† | ||||||
| Non-smoking | 857 | 3438 | 1 | |||
| Smoking | 302 | 1263 | 1.0 (0.8 to 1.1) | |||
| Missing | 198 | 727 | ||||
| Apgar at 5 minutes | ||||||
| ⩽6 | 5 | 27 | 0.7 (0.3 to 1.9) | 34 | 200 | 0.7 (0.5 to 1.0) |
| 7–8 | 12 | 37 | 1.3 (0.7 to 2.5) | 100 | 413 | 1.0 (0.8 to 1.2) |
| 9–10 | 237 | 950 | 1 | 2807 | 11 231 | 1 |
*Multiple births not included. †Registration not started until 1983, which is why numbers are smaller than for other exposures. The proportion of data that was missing was similar for cases and controls. Data on maternal civil status were missing for 6% of rheumatoid arthritis (RA) cases/controls and for 11% of juvenile idiopathic arthritis (JIA) cases/controls. Data on malformations were missing for 6% of all cases and controls. Data on Apgar scores were missing for 11% of JIA cases/controls and for 23% of RA cases/controls. For all other parameters, data were missing for less than 5% of all observations. AGA, appropriate for gestational age; LGA, large for gestational age; OR, odds ratio; SGA, small for gestational age.