Table 4.
Association between air pollutants and childhood asthma/wheezing after adjusting for preceding cyclic pollutants.
| Association | Model 1, HRa (95% CI) | Model 2b, adjusted HR (95% CI) |
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| Grouped by clinical staging |
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First trimester | 1.22 (1.00-1.48)c | N/Ad |
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Second trimester | 1.24 (1.04-1.47)c | 1.41 (1.13-1.77) |
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Third trimester | 1.10 (0.89-1.36)c | 1.04 (0.83-1.31) |
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| Grouped by lung development | |||||
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The embryonic stage | 1.02 (0.85-1.24)e | N/A |
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The pseudoglandular stage | 1.24 (1.03-1.51)e | 1.45 (1.13-1.86) |
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The canalicular stage | 1.23 (1.01-1.50)e | 1.30 (1.03-1.64) |
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The saccular stage | 1.08 (0.89-1.32)c | 1.03 (0.83-1.28) |
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The alveolar stage | 0.98 (0.82-1.18)c | 0.94 (0.77-1.15) |
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| Postnatal |
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First year | 1.65 (1.30-2.10)e | 1.77 (1.36-2.29) |
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First 2 years | 2.53 (2.16-2.96)e | 3.66 (3.05-4.38) |
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aHR: hazard ratio.
bWe adjusted the pollutants for the period preceding each period based on model 1. For example, air pollutants from the first trimester were included as covariates in the model for the second trimester, and air pollutants from both the first and second trimesters were included as covariates in the model for the third trimester. Air pollutants from the embryonic stage were added to the covariates in the model for the pseudoglandular stage, while contaminants from both the embryonic and pseudoglandular stages were added to the covariates in the model for the canalicular stage to adjust the model. Contaminants from the previous 3 periods were added to the covariates in the saccular stage model to adjust the model, and contaminants from the previous 4 periods were added to the covariates in the model for the alveolar stage to adjust the model. We also added pollutant exposure throughout pregnancy as a covariate in the first year and first 2 postnatal year models for adjustment.
cThere is a potential collinearity between temperature and air pollutants. The adjusted covariates do not include temperature.
dN/A: not applicable.
eAdjusted for temperature, maternal age, gravidity, parity, maternal occupation, yearly income per capita, passive smoking, maternal diet, history of asthma, gestational diabetes mellitus, premature, and season of conception.