Background: The knowledge about air pollution effects on birth weight, prematurity and small for gestational age [SGA] in low-exposure areas is insufficient. Objectives: The aim of this birth cohort study was to investigate if low-level exposure to air pollution was associated with prematurity and foetal growth and if there are gender specific effects. Method: We combined high quality registry information on 81110 births with individually modeled exposure data at residence for nitrogen oxides [NOx] and proximity to roads with differing traffic density. The data were analyzed by using logistic and linear regression with and without potential confounders. Results: An increased risk for babies being SGA was observed when highest and lowest NOx quartiles were compared, adjusting for maternal age, smoking, gender and year of birth. After additional adjustment for maternal country of origin and parity (which were highly intercorrelated), the increase was no longer statistically significant. However, in subgroup analysis when highest and lowest NOx quartiles were compared, there was still an increased risk for SGA for baby girls Odds Ratio [OR] 1.12 (95% Confidence Interval [CI] 1.01, 1.24), and also if mothers had not changed residency during pregnancy OR 1.09 (95% CI 1.01, 1.18). The confounders with the greatest impact on SGA were parity and country of origin. Concerning prematurity, the prevalence was lower in the three higher NOx exposure quartiles compared to the lowest category. Conclusion: For future studies on air pollution effects on birth outcomes careful control of confounding is crucial.
- Miljömedicin och yrkesmedicin