Ebba Malmqvist Division of Occupational and Environmental Medicine, Lund University, SE Lund, Sweden Emission database for NOx Maternal Exposure to Air Pollution and Birth Outcomes Objective It has been clearly stated that future research on air pollution and birth outcomes will have to confirm that the air pollution effects on birth weights, prematurity and SGA are genuine, causal and not due to confounding factors and to investigate if the effect also remains in low- exposure areas Aim To confirm that air pollution effects on birth weight, prematurity and small for gestational age [SGA] are genuine and causal and to investigate if the effect also remains in low-exposure areas and after adjusting for known confounders. Method We combined high quality registry information on unselected birth outcomes (81110 births) with individual-based modeled exposure data with high temporal and spatial resolution using nitrogen oxides [NOx] as a proxy for combustion-related air pollution as well as each mother’s proximity to roads with differing traffic density. The data were analyzed by using logistic and linear regression with and without potential confounders. Results The unadjusted OR for babies being SGA in the highest exposure quartile of NOx compared to the lowest was 1.37 (95% CI 1.28, 1.47). However when we adjusted for potential confounders, the elevated risk of babies being SGA observed in unadjusted models did not remain statistically significant, except when stratifying for mothers who had not moved home during pregnancy OR 1.09 (95% CI 1.01, 1.18) and for baby girls OR 1.12 (95% CI 1.01, 1.24) when mothers had lived in the highest exposure quartile of NOx compared to the lowest. The confounders with the greatest impact were parity and country of origin. Concerning prematurity, the prevalence was lower in the three higher NOx exposure quartiles compared to the reference category. Conclusion For future studies it is important to control for confounders and to investigate the impact of maternal country of origin and parity in research on air pollution effects on birth outcomes. Acknowledgments Special thanks to Lund University and its Medical Faculty, to Formas, the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning, and to Skåne Regional Council for funding this research. Upcoming future research will be on Type1 Diabetes and Air Pollution. Ebba Malmqvist, Anna Rignell-Hydbom, Håkan Tinnerberg, Jonas Björk, Emilie Stroh, Kristina Jakobsson, Ralf Rittner, Lars Rylander Exposure quartiles of NO x ( µ g/m 3 ) OR for SGA UnadjustedOR for SGA Adjusted for maternal age, smoking, birth year, gender and parity OR for SGA Adjusted for maternal age, smoking, birth year, gender and cointry of origin OR for SGA Adjusted for maternal age, smoking, birth year and gender, parity and country of origin (ref) ( ) 1.03 ( )0.99 ( ) ( )1.13 ( )1.10 ( )1.00 ( ) > ( )1.29 ( )1.21 ( )1.07 ( )