Table 1.

Characteristics of the Oslo Birth Cohort at Birth and at Two and Four Years Follow-Up


At Birth
(n = 3754)
%
2 Years
Follow-Up
(n = 2985)
%
4 years
Follow-Up
(n = 2531)
%
Gender (male)51.851.351.3
Parental atopy33.733.934.6
Birth weight
<3000 g12.612.312.0
3000–3499 g32.431.631.5
+3500 g55.156.156.4
Birth order
First51.452.652.6
Second36.335.735.7
Third or later12.211.711.7
Breastfeeding after 6 mo70.171.2
Maternal age at delivery
<25 y12.210.59.5
25–29 y36.235.735.5
+30 y51.653.855.0
Maternal education
<12 y7.35.64.7
12–15 y39.538.036.4
>15 y53.256.458.9
Family income per year
<200 000 NOK17.014.113.2
200 000–500 000 NOK64.766.866.8
>500 000 NOK18.319.120.0
Single parenthood
(at 6 mo age)
7.77.1
Pets at home
(at 6 mo age)
20.219.9
Day care outside the home (at 1 y)15.015.0
Environmental tobacco smoke exposure in early life43.641.339.8
Bronchial obstruction 0–2 y of life8.88.9
1 or more lower respiratory infection first y of life16.716.2
  • NOK indicates Norwegian Kroner.

    Maximal number of subjects with missing data in the baseline questionnaire: 78 (family income per year), in the 2-year questionnaire: 101 (breastfeeding), and in the 4-year questionnaire: 79 (breastfeeding).