Characteristics of children with an ASD diagnosis and their mothers, Denmark 1995–2003
| No ASD | ASD | p Value | |
| Maternal age | <0.001 | ||
| 20–24 | 81 996 (14.0) | 550 (15.2) | |
| 25–29 | 218 242 (37.3) | 1259 (34.8) | |
| 30–34 | 199 901 (34.2) | 1218 (33.7) | |
| 35–39 | 74 442 (12.7) | 508 (14.0) | |
| 40+ | 10 749 (1.8) | 84 (2.3) | |
| Parity | <0.001 | ||
| Primiparous | 248 429 (42.4) | 1801 (49.8) | |
| Multiparous | 336 896 (57.6) | 1818 (50.2) | |
| Educational level (years) | <0.001 | ||
| Lower (9–10) | 115 139 (22.7) | 906 (27.0) | |
| Intermediate (11–16) | 349 884 (69.0) | 2145 (63.8) | |
| Higher (17+) | 42 283 (8.3) | 310 (9.2) | |
| Smoking | <0.001 | ||
| Non-smoker | 454 685 (78.0) | 2713 (75.3) | |
| Smoker or stopped in pregnancy | 128 009 (22.0) | 889 (24.7) | |
| Multiplicity | 0.028 | ||
| Singletons | 561 598 (96.1) | 3501 (96.9) | |
| Twins | 22 389 (3.8) | 107 (3.0) | |
| Triplets | 703 (0.1) | 7 (0.1) | |
| Quadruplets | 21 (0.0) | 0 (0.0) | |
| Gestational age (weeks) | <0.001 | ||
| 20–27 | 1624 (0.3) | 20 (0.5) | |
| 28–31 | 4114 (0.7) | 29 (0.8) | |
| 32–36 | 31 268 (5.4) | 228 (6.4) | |
| 37–41 | 496 232 (85.3) | 2996 (83.5) | |
| 42+ | 48 158 (8.3) | 315 (8.8) | |
| Birth weight (g) | <0.001 | ||
| 500–1499 | 500 (0.9) | 44 (1.2) | |
| 1500–2499 | 24 414 (4.2) | 196 (5.5) | |
| 2500+ | 550 889 (94.9) | 3346 (93.3) | |
Data shown as numbers (percentages). Children without autism spectrum disorders (ASD) compared with children with ASD.