Demographic and socioeconomic characteristics of study participants
| Total cohort | Asthmatic children | Nonasthmatic children | |
| Subjects | 761 172 | 110 981 | 650 191 |
| Maternal age years | 30.0±5.5 | 30.1±5.5 | 30.0±5.5 |
| Gestational age weeks | 38.9±1.8 | 38.6±2.1 | 38.9±1.7 |
| Birthweight g | 3387.0±549.6 | 3327.9±596.3 | 3397.9±540.6 |
| Infant sex | |||
| Male | 390 665 (51.3) | 67 171 (60.5) | 323 484 (49.8) |
| Female | 370 507 (48.7) | 43 810 (39.5) | 326 697 (50.2) |
| Parity | |||
| 0 | 385 336 (50.6) | 55 777 (50.3) | 329 559 (50.7) |
| 1 | 259 543 (34.1) | 39 004 (35.1) | 220 539 (33.9) |
| ≥2 | 116 293 (15.3) | 16 200 (14.6) | 100 093 (15.4) |
| Intention to breastfeed | |||
| Yes | 606 236 (79.6) | 87 503 (78.8) | 518 733 (79.8) |
| No | 64 787 (8.5) | 9607 (8.7) | 55 180 (8.5) |
| Missing | 90 149 (11.8) | 13 871 (12.5) | 76 278 (11.7) |
| Maternal smoking status during pregnancy | |||
| Yes | 79 718 (10.5) | 11 398 (10.3) | 68 320 (10.5) |
| No | 597 907 (78.6) | 86 761 (78.2) | 511 146 (78.6) |
| Missing | 83 547 (11.0) | 12 822 (11.6) | 70 725 (10.9) |
| Maternal asthma | |||
| Yes | 45 443 (6.0) | 9299 (8.4) | 36 144 (5.6) |
| No | 715 729 (94.0) | 101 682 (91.6) | 614 047 (94.4) |
| Median family income | |||
| Quintile 1 | 149 838 (19.7) | 23 566 (21.2) | 126 272 (19.4) |
| Quintile 2 | 149 405 (19.6) | 21 798 (19.6) | 127 607 (19.6) |
| Quintile 3 | 150 339 (19.8) | 20 974 (18.9) | 129 365 (19.9) |
| Quintile 4 | 149 788 (19.7) | 21 826 (19.7) | 127 962 (19.7) |
| Quintile 5 | 149 872 (19.7) | 21 115 (19.0) | 128 757 (19.8) |
| Missing | 11 930 (1.6) | 1702 (1.5) | 10 228 (1.6) |
| Percentage of females who completed post-secondary education (age ≥25 years) | |||
| Quintile 1 | 124 580 (19.7) | 16 649 (18.0) | 107 931 (20.0) |
| Quintile 2 | 125 085 (19.8) | 18 278 (19.7) | 106 807 (19.8) |
| Quintile 3 | 124 050 (19.6) | 18 663 (20.1) | 105 387 (19.5) |
| Quintile 4 | 124 767 (19.7) | 18 932 (20.4) | 105 835 (19.6) |
| Quintile 5 | 124 508 (19.7) | 18 848 (20.3) | 105 660 (19.6) |
| Missing | 8966 (1.4) | 1310 (1.4) | 7656 (1.4) |
| Percentage visible minority | |||
| Quintile 1 | 149 652 (19.7) | 16 203 (14.6) | 133 449 (20.5) |
| Quintile 2 | 149 888 (19.7) | 18 687 (16.8) | 131 201 (20.2) |
| Quintile 3 | 149 768 (19.7) | 21 185 (19.1) | 128 583 (19.8) |
| Quintile 4 | 149 744 (19.7) | 24 620 (22.2) | 125 124 (19.2) |
| Quintile 5 | 149 777 (19.7) | 28 527 (25.7) | 121 250 (18.6) |
| Missing | 12 343 (1.6) | 1759 (1.6) | 10 584 (1.6) |
Data are presented as n, mean±sd or n (%).