Characteristics of population controls and patient groups, reported as n (%) unless specified as mean (SD)
| Characteristic | Population controls | axSpA | P value* | PsA | P value* |
| Singleton births 2010–2019 | 575 798 | 312 | 121 | ||
| Maternal age (years), mean (SD) | 30.6 (5.1) | 31.7 (4.3) | <0.001 | 32.0 (4.7) | 0.003 |
| <35 | 460 720 (80.0) | 242 (77.6) | 0.31 | 87 (71.9) | 0.034 |
| ≥35 | 115 077 (20.0) | 70 (22.4) | 34 (28.1) | ||
| Missing | 0 | 0 | 0 | ||
| Parity | |||||
| No children | 244 354 (42.4) | 141 (45.2) | 0.35 | 48 (39.7) | 0.60 |
| ≥1 child | 331 444 (57.6) | 171 (54.8) | 73 (60.3) | ||
| Missing | 0 | 0 | 0 | ||
| Smoking in pregnancy | 34 237 (6.7) | 19 (6.3) | 0.87 | 9 (8.0) | 0.74 |
| Missing | 67 663 | 12 | 8 | ||
| BMI first trimester, mean (SD) | 24.4 (4.8) | 25.1 (5.0) | 0.020 | 26.9 (5.6) | <0.001 |
| ≥25.0 | 138 056 (34.5) | 89 (40.3) | 0.09 | 49 (58.3) | <0.001 |
| ≥30.0 | 49 167 (12.3) | 33 (14.9) | 0.28 | 25 (29.8) | <0.001 |
| Missing | 176 090 | 91 | 37 | ||
| Previous CS | 55 992 (9.7) | 32 (10.3) | 0.83 | 15 (12.4) | 0.40 |
| Missing | 0 | 0 | 0 | ||
| Diabetes† | 25 924 (4.5) | 17 (5.4) | 0.50 | 8 (6.6) | 0.37 |
| Missing | 0 | 0 | 0 | ||
| ART‡ | 20 121 (3.5) | 15 (4.8) | 0.27 | 18 (14.9) | <0.001 |
| Missing | 0 | 0 | 0 |
*P value for patient group compared with population controls.
†Pregestational or gestational.
‡Assisted reproductive technology.
ART, assisted reproductive technology; axSpA, axial spondyloarthritis; BMI, body mass index; CS, caesarean section; PsA, psoriatic arthritis.