Table 1. Characteristics of the participating infants.
| Individual characteristics | Number (n/d)* | Percentage (%) or mean ± SD |
| Male gender | 229/412 | 55.6 |
| Gestational age at birth, weeks | 39.2±1.2 | |
| Maternal education level | ||
| Low | 300/393 | 76.3 |
| High† | 93/393 | 23.7 |
| Mother’s age at delivery, years | 32.3±3.5 | |
| Pre-pregnancy maternal body-mass index | 20.8±2.7 | |
| Prenatal smoking | ||
| No | 150/384 | 39.1 |
| Passive | 234/384 | 60.9 |
| Prenatal exposure to pets | 11/381 | 2.9 |
| Prenatal exposure to antibiotics | 38/384 | 9.9 |
| Mode of delivery | ||
| Vaginal | 210/311 | 67.5 |
| Cesarean section | 101/311 | 32.5 |
| History of parental allergic diseases | 178/373 | 47.7 |
| Older sibling(s) | 138/390 | 35.4 |
| Atopic dermatitis ever | 116/412 | 28.2 |
*n, number of children with each characteristic; d, the total number of children with information available on this characteristic.
†
graduated from graduate school.