Preterm birth and exposure to air pollutants during pregnancy

Background

Research has shown that prenatal exposure to air pollutants may have a detrimental effect on fetal development, with the strength of the relationship depending on the effect being studied. The evidence to date, however, is insufficient to establish a direct causal link between such exposure and preterm delivery. This study evaluates the specific effect of prenatal exposure to NO₂ and benzene on preterm births.

Methods

The population under study comprised 785 pregnant women who formed part of the INMA cohort in Valencia, Spain (2003–2005). Multiple regression models were used for mapping outdoor nitrogen dioxide (NO₂) and benzene levels throughout the area. Individual exposure was assigned as the estimated outdoor levels at each woman’s home measured during each trimester as well as throughout the entire pregnancy. Odds ratios (OR) and 95% confidence intervals (95% CI) were calculated in order to assess the association between preterm birth and exposure to NO₂ and benzene. The shape of the exposure–response curve between air pollution and the risk of preterm birth was analyzed with a flexible approach, introducing a natural cubic spline for air pollution levels into the model.

Results

Pregnant women exposed to NO₂ and benzene have an increased risk of preterm birth. This risk was shown to be significant when women were exposed to NO₂ levels >46.2 μg/m³ during the second and third trimesters as well as throughout the entire pregnancy and to benzene levels >2.7 μg/m³ throughout the entire pregnancy.

Conclusion

These results suggest that maternal exposure to traffic-related air pollution is associated with preterm birth.