Table 1.
Characteristics of the study participants by rheumatoid arthritis (N=111 706)
| Non-exposed (n=40 038) |
Prenatal-exposed (n=22 413) |
Infant-exposed (n=14 899) |
Preschool-exposed (n=34 356) | |
| Age, years, mean±SD | 42.48±1.23 | 45.43±1.29 | 47.69±1.14 | 49.12±1.24 |
| RA, n (%) | 541 (1.35) | 326 (1.45) | 289 (1.94) | 619 (1.80) |
| Diagnosis year, mean±SD | 31.78±8.92 | 32.95±9.92 | 34.74±10.69 | 34.85±11.01 |
| Region, n (%) | ||||
| Urban | 22 589 (56.42) | 11 307 (50.45) | 7076 (47.49) | 15 367 (44.73) |
| Non-severe | 13 556 (60.01) | 6833 (60.43) | 4111 (58.10) | 9073 (59.04) |
| Severe | 9033 (39.99) | 4474 (39.57) | 2965 (41.90) | 6294 (40.96) |
| Rural | 17 449 (43.58) | 11 106 (49.55) | 7823 (52.51) | 18 989 (55.27) |
| Non-severe | 3266 (18.72) | 2699 (24.30) | 1559 (19.93) | 4283 (22.56) |
| Severe | 14 183 (81.28) | 8407 (75.70) | 6264 (80.07) | 14 706 (77.44) |
| Sex, n (%) | ||||
| Male | 15 182 (37.92) | 8723 (38.92) | 6021 (40.41) | 13 597 (39.58) |
| Female | 24 856 (62.08) | 13 690 (61.08) | 8878 (59.59) | 20 759 (60.42) |
| Highest education, n (%) | ||||
| No formal school | 2058 (5.14) | 3658 (16.32) | 2127 (14.28) | 6507 (18.94) |
| Primary school | 7023 (17.54) | 5809 (25.92) | 3696 (24.81) | 9413 (27.40) |
| Middle school | 17 625 (44.02) | 6672 (29.77) | 4540 (30.47) | 9945 (28.95) |
| High school | 10 450 (26.10) | 5296 (23.63) | 3891 (26.12) | 6980 (20.32) |
| Technical school/college | 1894 (4.73) | 717 (3.20) | 475 (3.19) | 1099 (3.20) |
| University | 989 (2.47) | 258 (1.15) | 170 (1.14) | 412 (1.20) |
| Household income (¥), n (%) | ||||
| <2500 | 320 (0.80) | 193 (0.86) | 170 (1.14) | 392 (1.14) |
| 2500–4999 | 1634 (4.08) | 840 (3.75) | 691 (4.64) | 1636 (4.76) |
| 5000–9999 | 7059 (17.63) | 3783 (16.88) | 2599 (17.44) | 5959 (17.34) |
| 10 000–19 999 | 12 196 (30.46) | 7076 (31.57) | 4664 (31.30) | 10 245 (29.82) |
| 20 000–34 999 | 11 351 (28.35) | 6406 (28.58) | 4232 (28.40) | 9395 (27.35) |
| ≥35 000 | 7479 (18.68) | 4115 (18.36) | 2543 (17.07) | 6729 (19.59) |
| Alcohol consumption, n (%) | ||||
| Non-drinker | 16 528 (41.28) | 8983 (40.08) | 6118 (41.06) | 14 802 (43.08) |
| Ex-regular | 276 (0.69) | 197 (0.88) | 174 (1.17) | 414 (1.21) |
| Occasional drinker | 14 410 (35.99) | 7968 (35.55) | 5162 (34.65) | 11 522 (33.54) |
| Monthly | 1814 (4.53) | 1060 (4.73) | 558 (3.75) | 1252 (3.64) |
| Reduced intake | 657 (1.64) | 408 (1.82) | 302 (2.03) | 693 (2.02) |
| Weekly | 6354 (15.87) | 3797 (16.94) | 2585 (17.35) | 5673 (16.51) |
| Tobacco use, n (%) | ||||
| Non-smoker | 26 141 (65.29) | 14 248 (63.57) | 9183 (61.64) | 21 432 (62.38) |
| Occasional smoker | 2338 (5.84) | 1213 (5.41) | 789 (5.30) | 1724 (5.02) |
| Ex-smoker | 1205 (3.01) | 843 (3.76) | 646 (4.34) | 1502 (4.37) |
| Frequent smoker | 10 358 (25.87) | 6110 (27.26) | 4281 (28.73) | 9698 (28.23) |
| MET, hours/day | 25.83±13.94 | 24.93±14.03 | 23.56±14.15 | 23.86±14.00 |
| BMI, mean±SD | 23.81±3.23 | 23.96±3.20 | 24.02±3.24 | 23.95±3.25 |
| BMI <24, n (%) | 22 063 (55.11) | 11 826 (52.76) | 7744 (51.98) | 18 106 (52.70) |
| BMI ≥24, n (%) | 17 975 (44.89) | 10 587 (47.24) | 7155 (48.02) | 16 250 (47.30) |
BMI, body mass index; MET, metabolic equivalent of task hours; RA, rheumatoid arthritis.