Does socioeconomic status modify the effect of air pollution on birth outcomes?

Abstract

BACKGROUND: Several studies have examined whether air pollution is associated to adverse births outcomes but it is not clear if socioeconomic status (SES) modifies this relationship. OBJECTIVES: We investigated if individual and area-level socioeconomic status modified the relationship between ozone, nitrogen dioxide and particulate matter with aerodynamic diameter <10µm (PM10) and preterm deliveries (gestational age <37 weeks) and term low birth weight (TLBW; < 2500g). METHODS: Analyses were based on almost 1 million singleton live births in São Paulo municipality between 2011 and 2016. Exposure to PM10, NO2 and O3 were estimated by average trimestral and entire gestation based on date of birth and using daily averages of air pollution from the network of monitoring stations. Multilevel logistic regression models were conducted to examine the effect of air pollutants on both birth outcomes and whether it was modified by SES. RESULTS: In fully adjusted models, over the entire pregnancy, a 10µg/m³ increase in O3 and PM10 was associated to PTD (odds ratio; OR = 1.14 CI 1.13,1.16 and 1.08 CI = 1.02,1.15 respectively) and PM10 was associated to TLBW (OR = 1.08 CI 1.03, 1.14). Associations were modified by individual and area-level SES for both outcomes (p<0,001). Mothers with low individual SES had an additional risk for PTD and TLBW associated with PM10 exposure (OR = 1.04 CI 1.04,1.05 and 1.10 CI 1.08,1.14 respectively). Lower area-level SES also implied in a stronger risk for TLBW (OR = 1.05 CI 1.03,1.06). Similar effect modifications were observed for O3 exposure. Trimester specific associations were weaker but followed a similar pattern. CONCLUSION: Individual and neighborhood socioeconomic status modifies the effect of air pollution on adverse birth outcomes. Mothers with lower SES may be more susceptible to adverse pregnancy outcomes associated with air pollution exposure.