General characteristics of the eligible study population
| Baseline characteristics | Eligible study population (N=848) | FENO (N=306) | Rint (N=482) | Specific IgE (N=380) | |
| n/N | % | % | % | % | |
| Gender (female) | 391/848 | 46 | 47 | 47 | 41** |
| Allergic mother | 567/848 | 67 | 66 | 66 | 72** |
| Allergic father | 289/846 | 34 | 35 | 35 | 35 |
| Maternal education level | |||||
| Low | 195/832 | 23 | 21 | 20 | 23 |
| Middle | 366/832 | 44 | 41 | 43 | 43 |
| High | 271/832 | 33 | 38* | 36* | 34 |
| Caesarean section | 86/834 | 10 | 10 | 11 | 7** |
| Pets in the house (at birth) | 473/844 | 56 | 54 | 55 | 54 |
| Older sibling present | 422/846 | 50 | 49 | 52 | 59** |
| Smoking during pregnancy† | 147/831 | 18 | 18 | 17 | 21* |
| Smoking in the house (at age 4)‡ | 191/798 | 24 | 26 | 23 | 24 |
| Symptoms at baseline (age 3–4) | |||||
| Wheeze | 379/848 | 45 | 47 | 45 | 48 |
| Shortness of breath | 385/848 | 45 | 48 | 46 | 47 |
| Cough at night§ | 592/848 | 70 | 73 | 70 | 69 |
| Symptoms at age 8 years | |||||
| Wheeze | 104/730 | 14 | 13 | 13 | 14 |
| Inhaled steroid use | 109/722 | 15 | 15 | 12** | 16 |
| Doctor's diagnosis of asthma¶ | 55/700 | 8 | 8 | 6** | 9 |
For each variable, children with and without available data were compared. Significance of differences was tested using a χ2 test.
*p<0.05; **p<0.01.
↵† Positive if mother reported smoking at least 4 weeks after estimated date of conception.
↵‡ Smoking in the child's house more than once a week.
↵§ In period without a cold, flu or chest infection.
↵¶ Defined as a parental report of a doctor's diagnosis of asthma ever, in combination with parental report of symptoms in the past 12 months.
FENO, fraction of exhaled nitric oxide; IgE, immunoglobulin E; Rint, interrupter resistance.