Table 1.
Cohort characteristics
| Section | Variable | Category | N | % |
| Maternal perinatal | Livebirths | 7206 | 100 | |
| Maternal asthma | Yes | 617 | 8.6 | |
| No | 6589 | 91.4 | ||
| Missing | 0 | 0 | ||
| Maternal atopy | Yes | 1305 | 18.1 | |
| No | 5901 | 91.9 | ||
| Missing | 0 | 0 | ||
| Maternal age at delivery | <20 years | 264 | 3.7 | |
| 20–35 years | 5521 | 76.6 | ||
| >35 years | 1406 | 19.5 | ||
| Missing | 15 | 0.2 | ||
| Mode of delivery | Vaginal | 4916 | 68.2 | |
| C-section | 2290 | 31.8 | ||
| Missing | 0 | 0 | ||
| Hypertensive disorders of pregnancy | Yes | 446 | 6.2 | |
| No | 6760 | 93.8 | ||
| Missing | 0 | 0 | ||
| Gestational diabetes | Yes | 471 | 6.5 | |
| No | 6699 | 93.0 | ||
| Missing | 36 | 0.5 | ||
| Antibiotic use during pregnancy | Yes | 2259 | 31.4 | |
| No | 4947 | 68.7 | ||
| Missing | 0 | 0 | ||
| Smoking during pregnancy | Yes | 1223 | 17.0 | |
| No | 5953 | 82.6 | ||
| Missing | 30 | 0.4 | ||
| Socioeconomic deprivation—material | Q1-3 | 3696 | 51.3 | |
| Q4-5 | 3221 | 44.7 | ||
| Missing | 289 | 4.0 | ||
| Socioeconomic deprivation—social | Q1-3 | 3633 | 50.4 | |
| Q4-5 | 3284 | 45.6 | ||
| Missing | 289 | 4.0 | ||
| Child perinatal | Singletons | 6947 | 96.4 | |
| Multiple births | 259 | 3.6 | ||
| Sex | Male | 4639 | 64.4 | |
| Female | 2566 | 35.6 | ||
| Missing | 1 | 0.0 | ||
| Birth weight | Low (<2500 g) | 714 | 9.9 | |
| Adequate (>2500 g) | 6486 | 90.0 | ||
| Missing | 6 | 0.1 | ||
| Gestational age at birth | Term (≥37 weeks) | 6276 | 87.1 | |
| Pre-term (<37 weeks) | 929 | 12.9 | ||
| Missing | 1 | 0.0 | ||
| Birth weight percentiles | SGA | 768 | 10.7 | |
| AGA | 5767 | 80.0 | ||
| LGA | 670 | 9.3 | ||
| Missing | 1 | 0.0 | ||
| Season at birth | Spring (Mar–Apr) | 1775 | 24.6 | |
| Summer (Jun–Aug) | 1817 | 25.2 | ||
| Fall (Sep–Nov) | 1820 | 25.3 | ||
| Winter (Dec–Feb) | 1794 | 24.9 | ||
| Missing | 0 | 0 | ||
| Early life | Neonatal jaundice requiring phototherapy | Yes | 451 | 6.3 |
| No | 6755 | 93.7 | ||
| Missing | 0 | 0 | ||
| Bronchopulmonary dysplasia | Yes | 84 | 1.2 | |
| No | 7122 | 98.8 | ||
| Missing | 0 | 0 | ||
| Hospitalisation for lower respiratory illness | Yes | 481 | 6.7 | |
| No | 6725 | 93.3 | ||
| Missing | 0 | 0 | ||
| Antibiotics use prior to asthma diagnosis | Yes | 5723 | 79.4 | |
| Antibiotics during respiratory illness* | 4242 | 59.9 | ||
| No | 1483 | 20.6 | ||
| Missing | 0 | 0 | ||
| Child atopy | Yes | 3834 | 53.2 | |
| No | 3372 | 46.8 | ||
| Missing | 0 | 0 | ||
| Age at diagnosis, years | Mean (95% CI) | 2.6 (2.6, 2.6) | ||
| Missing | 0 | 0 | ||
| Season at diagnosis | Spring (Mar–Apr) | 1602 | 22.2 | |
| Summer (Jun–Aug) | 1956 | 27.1 | ||
| Fall (Sep–Nov) | 1812 | 25.2 | ||
| Winter (Dec–Feb) | 1836 | 25.5 | ||
| Missing | 0 | 0 | ||
| Asthma control | Categories | Controlled | 3728 | 51.7 |
| Partly controlled | 2629 | 36.5 | ||
| Uncontrolled | 849 | 11.8 | ||
| Missing | 0 | 0 |
*Antibiotics dispensed within 2 weeks of a healthcare encounters associated with respiratory morbidity.