Characteristics of asthma cases and matched controls selected in the administrative databases(first stage of sampling)
| Childhood asthma cases | Controls | Crude RR (95% CI) | |
| Subjects n | 2681 | 30318 | |
| Control and severity of maternal asthma during pregnancy | |||
| Mild controlled | 1579 (58.9) | 19081 (62.9) | Reference# |
| Mild uncontrolled | 526 (19.6) | 5889 (19.4) | 1.09 (0.98–1.21) |
| Moderate-to-severe controlled | 7 (0.3) | 82 (0.3) | 0.99 (0.45–2.21) |
| Moderate-to-severe uncontrolled | 569 (21.2) | 5266 (17.4) | 1.29 (1.16–1.43) |
| Child | |||
| Male sex | 1551 (57.9) | 14299 (47.2) | 1.55 (1.42–1.68) |
| Small for gestational age | 426 (15.9) | 4567 (15.1) | 1.11 (0.97–1.28) |
| Allergic rhinitis | 73 (2.7) | 499 (1.7) | 1.63 (1.25–2.14) |
| Atopic dermatitis | 246 (9.2) | 2079 (6.9) | 1.44 (1.24–1.67) |
| ≥1 antibiotic prescription between birth and index date or within first 6 months of life | 1159 (43.2) | 9928 (32.8) | 1.59 (1.46–1.72) |
| Maternal socio-demographics | |||
| ≥35 yrs of age at conception | 176 (6.6) | 2506 (8.3) | 0.75 (0.63–0.88) |
| Mother receiving social welfare | 2344 (87.4) | 25712 (84.8) | 1.29 (1.13–1.46) |
| Education | |||
| Missing | 182 (6.8) | 2050 (6.8) | 1.56 (1.17–2.06) |
| <12 yrs | 1656 (61.8) | 18300 (60.4) | 1.50 (1.18–1.91) |
| 12–15 yrs | 763 (28.4) | 8726 (28.8) | 1.47 (1.15–1.88) |
| >15 yrs | 80 (3.0) | 1242 (4.1) | Reference |
| Living in rural area | 484 (18.1) | 5765 (19.0) | 0.94 (0.84–1.04) |
| Pregnancy | |||
| Pre-natal visits n | |||
| 0–5 | 402 (15.0) | 4942 (16.3) | 0.91 (0.81–1.03) |
| 6–16 | 2141 (79.9) | 23873 (78.7) | Reference |
| >16 | 138 (5.1) | 1503 (5.0) | 1.09 (0.88–1.34) |
| >1 obstetrician visit during pregnancy | 2243 (83.7) | 25155 (83.0) | 1.03 (0.92–1.16) |
| Mode of delivery | |||
| Vaginal delivery | 2113 (78.8) | 24439 (80.6) | Reference |
| Unplanned Caesarean section | 289 (10.8) | 3213 (10.6) | 1.01 (0.88–1.15) |
| Planned Caesarean section | 279 (10.4) | 2666 (8.8) | 1.20 (1.05–1.38) |
| Pregnancy in preceding year | 877 (32.7) | 9576 (31.6) | 1.05 (0.96–1.15) |
| Intra-nasal corticosteroid use | 209 (7.8) | 2291 (7.6) | 1.05 (0.90–1.22) |
| Antibiotic prescriptions filed n | 0.97±1.13 | 0.82±1.05 | 1.13 (1.09–1.17)¶ |
| Maternal medical conditions | |||
| Chronic hypertension | 76 (2.8) | 726 (2.4) | 1.10 (0.86–1.42) |
| Pregnancy-induced hypertension | 161 (6.0) | 1881 (6.2) | 0.96 (0.81–1.14) |
| Diabetes mellitus | 72 (2.7) | 733 (2.4) | 1.12 (0.86–1.45) |
| Gestational diabetes | 220 (8.2) | 2484 (8.2) | 1.00 (0.86–1.17) |
Data are presented as n (%) or mean±sd, unless otherwise indicated. RR: rate ratio. #: reference category for variables composed of >2 categories; ¶: RR for each additional prescription. Values in bold are statistically significant. Note: Other asthma-related variables during pregnancy are presented in table 1⇓ of the online supplementary material as additional information. They are features of the definition of maternal asthma control and severity in pregnancy.