Maternal characteristics in RA, AxSpA, PSA and control pregnancies, n (%)
| N | RA | Controls* | AxSpA | Controls* | PsA | Controls* |
| 1739 | 17 390 | 819 | 8190 | 489 | 4890 | |
| Country | ||||||
| Sweden | 1104 (63.5) | 11 040 (63.5) | 431 (52.6) | 4310 (52.6) | 233 (47.6) | 2330 (47.6) |
| Denmark | 635 (36.5) | 6350 (36.5) | 388 (47.4) | 3880 (47.4) | 256 (52.4) | 2560 (52.4) |
| Maternal age (years) | ||||||
| ≤24 | 47 (2.7) | 470 (2.7) | 39 (4.8) | 390 (4.8) | 44 (9.0) | 440 (9.0) |
| 25–29 | 371 (21.3) | 3710 (21.3) | 230 (28.1) | 2300 (28.1) | 138 (28.2) | 1380 (28.2) |
| 30–34 | 678 (39.0) | 6780 (39.0) | 348 (42.5) | 3480 (42.5) | 169 (34.9) | 1690 (34.6) |
| >34 | 643 (37.0) | 6430 (37.0) | 202 (24.7) | 2020 (24.7) | 138 (28.2) | 1380 (28.2) |
| Calendar year of delivery | ||||||
| 2006–2009 | 242 (13.9) | 2420 (13.9) | 53 (6.5) | 530 (6.5) | 28 (5.7) | 280 (5.7) |
| 2010–2012 | 418 (24.9) | 4180 (24.0) | 128 (15.6) | 1280 (15.6) | 79 (16.2) | 790 (16.2) |
| 2013–2015 | 545 (31.3) | 5450 (31.3) | 294 (35.9) | 2940 (35.9) | 151 (30.9) | 1510 (30.9) |
| 2016–2018 | 534 (30.7) | 5340 (30.7) | 344 (42.0) | 3440 (42.0) | 231 (47.2) | 2310 (47.2) |
| Parity at time of conception | ||||||
| Nulliparous | 766 (44.0) | 7660 (44.0) | 369 (45.1) | 3690 (45.1) | 212 (43.4) | 2120 (43.4) |
| Primi/multiparous | 968 (55.7) | 9680 (55.7) | 450 (54.9) | 4500 (54.9) | 274 (56.0) | 2740 (56.0) |
| Missing | 5 (0.3) | 50 (0.3) | 0 (0.0) | 0 (0.0) | 3 (0.6) | 30 (0.6) |
| BMI (kg/m2) | ||||||
| <18.5 | 117 (6.7) | 1075 (6.2) | 58 (7.1) | 532 (6.5) | 23 (4.7) | 256 (5.2) |
| 18.5–24.9 | 822 (47.3) | 8433 (48.5) | 378 (46.2) | 3967 (48.4) | 199 (40.7) | 2383 (48.7) |
| 25.0–29.9 | 412 (23.7) | 3928 (22.6) | 200 (24.4) | 1854 (22.6) | 135 (27.6) | 1085 (22.2) |
| ≥30.0 | 211 (12.1) | 2130 (12.2) | 104 (12.7) | 1000 (12.2) | 81 (16.6) | 637 (13.0) |
| Missing | 177 (10.2) | 1824 (10.5) | 79 (9.6) | 837 (10.2) | 51 (10.4) | 529 (10.8) |
| Smoking | ||||||
| Non-smoker | 1576 (90.6) | 15 601 (89.7) | 724 (88.4) | 7320 (89.4) | 402 (82.2) | 4319 (88.3) |
| Smoker | 87 (5.0) | 971 (5.6) | 63 (7.7) | 511 (6.2) | 55 (11.2) | 332 (6.8) |
| Missing | 76 (4.4) | 818 (4.7) | 32 (3.9) | 359 (4.4) | 32 (6.5) | 239 (4.9) |
| Highest educational level | ||||||
| >12 years | 711 (40.9) | 6818 (39.2) | 459 (56.0) | 4529 (55.3) | 231 (47.2) | 2504 (51.2) |
| ≤12 years | 1019 (58.6) | 10 189 (58.6) | NA | 3454 (42.2) | NA | 2237 (45.7) |
| Missing | 9 (0.5) | 383 (2.2) | ≤3 | 207 (2.5) | ≤3 | 149 (3.0) |
| Disease duration at time of delivery | ||||||
| Years, median (IQR) | 6.5 (3.8, 10.2) | NA | 7.9 (4.5, 12.7) | NA | 7.0 (3.8, 11.2) | NA |
| Prepregnancy diabetes | ||||||
| Yes | 42 (2.5) | 174 (1.0) | 11 (1.3) | 84 (1.0) | 15 (3.1) | 49 (1.0) |
| Prepregnancy disease activity | ||||||
| HAQ, median (IQR) | 0.50 (0.00, 1.00) | NA | 0.38 (0.00, 0.88) | NA | 0.63 (0.13, 1.13) | NA |
| Missing, n | 794 | NA | 571 | NA | 256 | NA |
| Prepregnancy treatment | ||||||
| Untreated | ||||||
| No | 410 (23.6) | NA | 399 (48.7) | NA | 189 (38.7) | NA |
| CS | 145 (8.3) | NA | 33 (4.0) | NA | 23 (4.7) | NA |
| Monotherapy | ||||||
| csDMARD | 331 (19.0) | NA | 50 (6.1) | NA | 95 (19.4) | NA |
| bDMARD | 185 (10.6) | NA | 207 (25.3) | NA | 75 (15.3) | NA |
| CS+csDMARD | 228 (13.1) | NA | 18 (2.2) | NA | 19 (3.9) | NA |
| CS+bDMARD | 163 (9.4) | NA | 46 (5.6) | NA | 30 (6.1) | NA |
| Combination therapy | ||||||
| csDMARD+bDMARD | 134 (7.7) | NA | 44 (5.4) | NA | 38 (7.8) | NA |
| CS+csDMARD+ bDMARD | 143 (8.2) | NA | 22 (2.7) | NA | 20 (4.1) | NA |
Singleton pregnancies. One woman may contribute with one or more pregnancies.
*Matched 1:10 on maternal age, parity and year of delivery.
AxSpA, axial spondyloarthritis; bDMARD, biological disease-modifying antirheumatic drug; BMI, body mass index; CS, oral corticosteroids; csDMARD, conventional synthetic disease-modifying antirheumatic drug; HAQ, Health Assessment Questionnaire; NA, not applicable; PsA, psoriatic arthritis; RA, rheumatoid arthritis.