Table 1. Characteristics of infants who were included and excluded from the study.
| Participants (307) | Non-participants (1,426) | P value | |||
|---|---|---|---|---|---|
| Number | Mean±SD or % | Number | Mean±SD or % | ||
| Sex (male, %) | 171 | 55.7 | 673 | 51.8 | 0.228 |
| Gestational age (week) | 303 | 39.27±1.21 | 1,257 | 39.10±1.27 | 0.042 |
| Maternal age at birth (year) | 307 | 32.69±3.44 | 1,296 | 32.56±3.43 | 0.535 |
| Cesarean section delivery (%) | 90/269 | 33.5 | 377/1,117 | 33.8 | 0.943 |
| Maternal body mass index (kg/m2) | 307 | 20.53±2.24 | 1,352 | 20.66±2.63 | 0.369 |
| Maternal education state | 307 | 1,332 | 0.999 | ||
| ≤High school (%) | 21 | 6.8 | 90 | 6.8 | |
| University or college (%) | 218 | 71.0 | 947 | 71.1 | |
| Graduate school (%) | 68 | 22.2 | 295 | 22.2 | |
| Parental history of allergic disease (%) | 178/295 | 60.3 | 615/1,085 | 56.7 | 0.288 |
| Maternal ETS exposure during pregnancy (%) | 189/307 | 61.6 | 668/1,084 | 61.6 | 1.000 |
| Infantile ETS exposure at 1 year (%) | 75/241 | 31.1 | 196/600 | 32.7 | 0.684 |
| PM2.5 during pregnancy (µg/m3) | 307 | 6.08±7.64 | 307 | 5.70±4.97 | 0.461 |
| PM2.5 at 6 months of age (µg/m3) | 75 | 5.11±7.05 | 245 | 5.40±5.33 | 0.699 |
| Nrf2 GG genotype (%) | 123/307 | 40.1 | 351/913 | 38.4 | 0.636 |
| GSTP1 AG or GG genotype (%) | 113/306 | 36.9 | 295/919 | 32.1 | 0.124 |
| GSTM1 null genotype (%) | 173/305 | 56.7 | 490/911 | 53.8 | 0.388 |
| Incidence of LRTIs* at 1 year (%) | 49/300 | 16.3 | 111/637 | 17.4 | 0.917 |
| Incidence of URTIs† at 1 year (%) | 234/307 | 76.2 | 450/668 | 67.4 | 0.005 |
*Lower respiratory tract infections: tracheobronchitis, pneumonia, and bronchiolitis; †Upper respiratory tract infections: common cold, sinusitis, otitis media, and croup.
ETS, environmental tobacco smoke; GSTM1, glutathione S-transferase-mu 1; GSTP1, glutathione S-transferase-pi 1; Nrf2, nuclear factor erythroid 2-related factor; PM2.5, fine particulate matter; LRTIs, lower respiratory tract infections; URTIs, upper respiratory tract infections.