To assess the association between maternal exposure during the first trimester to air pollutantsparticulate matter ≤ 10 μm in aerodynamic size (PM₁₀), sulphur dioxide (SO₂), and nitrogen dioxide (NO₂) and birth weight in Shanghai.

The study was based on the singleton data retrieved from the official Shanghai birth registry system from 2008 to 2012 and on the daily air pollution records from the Shanghai Environmental Monitoring Center from 2007 to 2012. By using recorded gestational age and date of birth, the average air pollution level was calculated for the first trimester for each mother, and then the impacts of different levels of air pollution during the first trimester on birth weight were assessed.

The low birth weight rate was 2.78% in Shanghai in 5 years. There were significant differences in birth weight within the subgroups of infant's gender, year of birth, mother's age, and maternal education, gravidity, and parity (all Ps<0.01). There were significant differences in birth weight among the infants with different maternal exposure levels of PM₁₀, SO₂, and NO₂ during the first trimester (all P<0.01). After controlling for potential confounders, the results of linear regression analyses indicated that the mean concentrations of PM₁₀, SO₂, and NO₂ during the first trimester was associated with birth weight; A decrease of 4.3 g in birth weight was associated with an increase of 10 μg/m³ in the average level of PM₁₀ during the first trimester; A decrease of 7.6 g in birth weight was associated with an increase of 10 μg/m³ in the average level of SO₂ during the first trimester; A decrease of 6.0 g in birth weight was associated with an increase of 10 μg/m³ in the average level of NO₂ during the first trimester.

Exposure to selected air pollutants during the first trimester is associated with low birth weight. Therefore, the effects of air pollution on pregnancy outcome deserve concern.