Table 1. Distribution of characteristics among individuals with follow-up information available for the analysis of asthma at 36 months and current asthma at 7 years.
| Characteristic | Category | Sample current asthma at 36 months (N = 50,311) | Sample current asthma at 7 years (N = 24,827) |
|---|---|---|---|
| Maternal age at delivery (Mean (SD)) | NA | 30.4 (4.4) | 30.5 (4.3) |
| Maternal parity (%) | Primiparous | 48.2 | 45.8 |
| 1 | 33.9 | 34.9 | |
| 2 | 14.1 | 15.1 | |
| 3 or more | 3.8 | 4.2 | |
| Maternal education (%) | Less than high school | 5.3 | 5.4 |
| High school | 26.6 | 27.7 | |
| Up to 4 years of college | 43.3 | 44.9 | |
| More than 4 years of college | 24.8 | 22.0 | |
| Maternal yearly salary(%) | <200,000 NOK | 25.8 | 27.9 |
| 200–400,000 NOK | 61.8 | 62.6 | |
| >400,000 NOK | 12.5 | 9.5 | |
| Maternal height in cm (Mean (SD)) | NA | 168.3 (5.9) | 168.3 (5.9) |
| Maternal pre-pregnancy BMI (%) | Underweight (<18.5) | 2.9 | 2.7 |
| Normal weight (18.5–24.9) | 66.9 | 66.7 | |
| Overweight (25–29.9) | 21.6 | 22.1 | |
| Obese (> = 30) | 8.6 | 8.5 | |
| Paternal height in cm (Mean (SD)) | NA | 181.6 (6.4) | 181.6 (6.4) |
| Paternal BMI (%) | Underweight (<18.5) | 0.2 | 0.2 |
| Normal weight (18.5–24.9) | 46.1 | 46.2 | |
| Overweight (25–29.9) | 45.5 | 45.6 | |
| Obese (> = 30) | 8.3 | 8.0 | |
| Maternal smoking during pregnancy (%) | No | 92.7 | 92.5 |
| Yes | 7.3 | 7.5 | |
| Maternal folate intake during pregnancy (%) | None | 12.7 | 14.2 |
| Only first trimester | 24.1 | 21.8 | |
| Only after first trimester | 8.9 | 10.6 | |
| Both first trimester and after | 54.3 | 53.3 | |
| Maternal asthma (%) | No | 92.9 | 93.0 |
| Yes | 7.1 | 7.0 | |
| Paternal asthma(%) | No | 91.2 | 91.5 |
| Yes | 8.9 | 8.5 | |
| Child gender(%) | Male | 51.1 | 51.2 |
| Female | 48.9 | 48.8 | |
| Child gestational age in weeks (Mean (SD)) | NA | 39.5 (1.7) | 39.5 (1.7) |
| Breastfeeding 0–6 months(%) a | None | 2.5 | 2.5 |
| Partial | 52.7 | 51.7 | |
| Exclusive | 44.8 | 45.8 |
SD: standard deviation, BMI: body mass index
The amount of missing information on individual covariates was generally low (<2%).
a Breastfeeding the first 6 months characterized as partial if the mother reported giving the child breast milk and another source of milk (i.e. formula). Breastfeeding characterized as exclusive if the mother reported only giving the child breast milk throughout the first 6 months of life and no other source of milk (i.e. formula).