BackgroundRecent reports have shown that air pollution may increase the risk of adverse birth outcomes. We have evaluated the relationship between ambient air pollution and the occurrence of low birth weight and preterm delivery using routinely collected data in Lithuania.MethodsThis epidemiological study comprised all singleton newborns (N = 3,988), born to women in 1998, who resided in the City of Kaunas. Birth data and information on maternal characteristics were obtained from the Lithuanian National Birth Register. To estimate residential exposure levels, we used measurements of ambient nitrogen dioxide (NO2) and formaldehyde, which were collected at 12 monitoring posts. Multivariate logistic regression was used to estimate the effect that each pollutant would have on low birth weight (LBW) and premature birth while controlling for potential confounders.ResultsAdjusted odds ratios (OR) for LBW increased with increasing formaldehyde exposure (OR2nd tertile = 1.86, 95% CI 1.10–3.16; OR3rd tertile = 1.84, 95% CI 1.12–3.03). Adjusted ORs of preterm birth for the medium and high NO2 tertile exposures were OR = 1.14 (95% CI 0.77–1.68) and OR = 1.68 (95% CI 1.15–2.46), respectively. The risk of preterm birth increased by 25% (adjusted OR = 1.25, 95% CI 1.07–1.46) per 10 μg/m3 increase in NO2 concentrations. An analysis by trimester showed that pregnancy outcomes were associated with first-trimester exposure to air pollutants. However, there were no significant relationships in other pregnancy periods between preterm birth and exposure to formaldehyde or between LBW and NO2 exposure.ConclusionOur findings suggest that in the City of Kaunas there might be a relationship between maternal exposure to ambient formaldehyde and the risk of LBW, as well as between NO2 exposure and the risk of preterm birth.