Effect of outdoor air pollution and indoor environmental factors on small for gestational age

Background: Small for gestational age (SGA) is a major public health problem that affects 32.4 million infants worldwide and its prevalence is increasing rapidly in new-borns. However, the key risk factors and their exposure time window on the development of SGA are unclear. Objective: We aim to investigate the association between exposure to outdoor air pollution and indoor environmental factors during which critical timing window and SGA, and to evaluate which specific personal factors modify this association. Methods: A retrospective cohort study of 3509 infants was conducted in Changsha, China during 2011-2012. A questionnaire survey was performed to obtain the formation on infant's birth outcomes and prenatal exposure of indoor environmental factors containing parental (maternal and/or paternal) smoking, new furniture, house redecoration, mold or dampness, window condensation, and keeping dogs in gestational age. Intrauterine exposure to industrial air pollutant (SO2), traffic-related air pollutant (NO2) and inhalable particulate matter (PM10) was estimated during three trimesters and entire pregnancy. Associations between outdoor air pollutants and indoor environmental factors and SGA, term SGA (TSGA) and preterm SGA (PSGA) were assessed by multiple logistic regression model in terms of odds ratio (OR) and 95% confidence interval (CI). Results: Prevalence of SGA (5.2%) and TSGA (4.9%) were significantly associated with intrauterine exposure to outdoor SO2 during the entire gestational age with adjusted ORs (95% CI) of 1.08 (1.01-1.15) and 1.08 (1.00-1.15) for per 10 mu g/m(3) increase in SO2 exposure after adjusting for the covariates, indoor environmental factors, and outdoor air temperature, and PSGA prevalence (0.3%) was significantly related with PM10 exposure during whole pregnancy with odds = 2.21 (1.08-4.51). However, no association was observed for traffic-related air pollutant NO2 exposure. Specifically, the association was more significant for SO2 exposure during the 1st and/or 2nd trimester. We further found that TSGA and PSGA were associated with indoor exposure to parental smoking and new furniture, respectively, ORs (95% CI) = 1.46 (1.00-2.11) and 10.95 (1.46-81.95). We observed that the odds of SGA and TSGA attributed to SO2 exposure in the first two trimesters was only significant among families with parental smoking and new furniture in gestation. Sensitivity analysis showed that infants with female sex and born in cold months were more susceptible to the effect of outdoor SO2 exposure during the first two trimesters and entire gestational age on SGA and TSGA. On the other hand, infants born in the cold season and by a younger mother were more sensitive to the effect of indoor parental smoking in utero on SGA and TSGA. Conclusion: Maternal exposure to industry-related air pollution and indoor environmental risk factors during pregnancy, particularly during the first two trimesters, significantly increased SGA risk, and some specific personal factors could modify these associations.