[Relationship between air pollution exposure during pregnancy and birth weight of term singleton live-birth newborns]

Objective: This study explored the association between air pollution exposure and birth weight by using the multilevel linear model, after controlling related meteorological factors and individual differences of both mothers and babies. Methods: Women of childbearing age who were pregnant in Xi'an from 2010 to 2013, were selected as objects of this study. Multistage random sampling method was used to select 4 631 subjects followed by a self-designed questionnaire survey. Data related to quality of air and meteorology were gathered from routine monitoring system. Gestational age and date of birth, together with the average levels of air pollution were calculated for each trimester on each mother, and then the impact of air pollution on birth weight was assessed. A multilevel linear model was employed to investigate the association between the levels of exposure to air pollution by birth weight. Confounding factors were under control. We established three models in this study: Model 1 which involving the variable of air pollution exposure. Model 2 was adjusted for variables in Model 1 plus some other individual differences of both mother and baby. Model 3 was adjusted for variables in Model 2 plus meteorological factors. Results: There were significant differences seen in birth weight within the subgroups of gender, gestational age, mother's reproductive age, maternal education, residential areas and family incomes (P<0.01) of the infants. However, there was no difference found in Model 1 (P>0.05). Data from Model 3 indicated that a decrease of 13.3 g(10.9 g in Model 2) and 6.6 g (5.9 g in Model 2) in birth weight that were associated with an increase of 10 μg/m(3) in the average level of NO(2) and PM(10) during the second trimester; A decrease of 13.7 g (9.8 g in Model 2) in birth weight was associated with an increase of 10 μg/m(3) in the average level of NO(2) during the third trimester. Conclusion: After controlling for meteorological factors, the levels of exposure to NO(2) and PM(10) during the second trimester and NO(2) during the third trimester were negatively associated with birth weight.