General characteristics of the study population
| Dutch (n=3490) | Non-Dutch (n=131) | p value | |
|---|---|---|---|
| Mother ever asthma (%) | 7.2 | 6.2 | 0.4 |
| Atopic mother (%) | 29.4 | 35.1 | 0.2 |
| Father ever asthma (%) | 7.8 | 6.3 | 0.7 |
| Atopic father (%) | 30.3 | 29.2 | 0.8 |
| Sibling ever asthma (%) | 4.2 | 3.2 | 0.8 |
| Allergic sibling (%) | 25.7 | 28.1 | 0.6 |
| Gender male (%) | 51.8 | 50.4 | 0.8 |
| Smoking during pregnancy (%) | 18.6 | 22.4 | 0.5 |
| Smoke exposure in the home at age 1 (%) | 26.9 | 38.7 | 0.02 |
| Premature birth (<37 weeks of gestation) (%) | 4.8 | 7.3 | 0.4 |
| Mean birth weight (kg, SD) | 3.519 (0.542) | 3.271 (0.567) | <0.001 |
| Mean weight at age 1 (kg, SD) | 9.8 (1.1) | 9.7 (1.3) | 0.2 |
| Exclusive formula feeding at 3 months (%) | 52.7 | 50.4 | 0.7 |
| At least one sibling (%) | 51.7 | 46.4 | 0.3 |
| Day care at age 1 (%) | 65.5 | 61.7 | 0.7 |
| Crowding (<1.25 room/person) (%) | 41.0 | 53.2 | 0.007 |
| Exposure to pets (%) | 52.7 | 25.4 | <0.001 |
| Living in apartment (%) | 5.6 | 27.8 | <0.001 |
| Damp or mould spots in the home (%) | 13.6 | 23.3 | 0.009 |
| Carpet floor bedroom child (%) | 56.4 | 51.6 | 0.3 |
| Carpet floor bedroom parents (%) | 70.1 | 64.7 | 0.2 |
| Mechanical ventilation in the home (%) | 54.2 | 67.5 | 0.003 |
| Mean age mother of the child (years, SD) | 30.5 (3.7) | 28.8 (4.9) | <0.001 |
| Mean age father of the child (years, SD) | 32.8 (4.5) | 32.0 (5.3) | 0.1 |
| Groningen (%) | 32.8 | 11.5 | <0.001 |
| Utrecht (%) | 40.5 | 32.8 | |
| Rotterdam (%) | 26.6 | 55.7 | |
| Mother low level of education (%) | 12.6 | 21.4 | 0.01 |
| Father low level of education (%) | 19.3 | 22.0 | 0.5 |
| Mother unemployed (%) | 33.9 | 41.2 | 0.1 |
| Father unemployed (%) | 2.4 | 15.5 | <0.001 |
| Natural history study (%) | 82.5 | 80.9 | 0.5 |
| Intervention study active (%) | 9.5 | 8.4 | |
| Intervention study placebo (%) | 8.4 | 10.7 |