Table 1.
Distribution of covariates in children with asthma (cases) and control siblings
| Cases (N = 1,874) N (%) |
Controls (N = 1,847) N (%) |
P-value | |
|---|---|---|---|
| Child characteristics | |||
| Male gender | 1,110 (59) | 843 (45) | <0.001 |
| Mean age at first asthma diagnosis | 3.6 years | NA | NA |
| Mean number of asthma drugs in 12 months | 15 | 0 | NA |
| First-born | 991 (53) | 728 (39) | <0.001 |
| Use of antacids prior to index date | 22 (1.2) | 29 (1.7) | 0.32 |
| Low birth weight/prematurity | 28 (1.5) | 18 (1.0) | 0.14 |
| Pregnancy characteristics | |||
| Mean age (SD) in years | 27.9 (5.2) | 28.6 (5.2) | <0.001 |
| Presence of asthma | 89 (5) | 90 (5) | 0.94 |
| Presence of migraine | 33 (2) | 32 (2) | 0.90 |
| Presence of (pre-)eclampsia | 1 (0.05) | 0 (0) | 0.32 |
| High BMI (>35)a | 148 (10) | 165 (11) | 0.39 |
| Current smokerb | 470 (29) | 459 (28) | 0.51 |
| Mean number of GP visits during pregnancy | 11.4 (7.4) | 11.9 (7.6) | 0.03 |
| Use of paracetamol | 256 (14) | 259 (14) | 0.89 |
| Use of NSAIDs | 49 (3) | 50 (3) | 0.91 |
BMI body mass index, GP general practitioner, NA not applicable, NSAIDs non-steroidal anti-inflammatory drugs, SD standard deviation
aData on BMI were missing for 877 patients
bData on smoking were missing for 528 patients