Risk of particulate matter on birth outcomes in relation to maternal socio-economic factors: a systematic review

Abstract

A growing number of studies provide evidence of an association between exposure to maternal air pollution during pregnancy and adverse birth outcomes including low birth weight and preterm birth. Prevention of these health effects of air pollution is critical to reducing the adverse infant outcomes, which can have impacts throughout the life course. However, there is no consensus on whether the association between air pollution exposure and birth outcomes varies by maternal risk factors including demographic characteristics and socio-economic status. Such information is vital to understand potential environmental health disparities. Our search found 859 unique studies, of which 45 studies met our inclusion criteria (Jan. 2000- July. 2019). We systematically reviewed the 45 identified epidemiologic studies and summarized the results on effect modifications by maternal race/ethnicity, educational attainment, income, and area-level socio-economic status. We considered adverse birth outcomes of preterm birth, low birth weight, small for gestational age (SGA), and stillbirth. Suggestive evidence of higher risk of particulate matter in infants of African-American/black mothers than infants of other women was found for preterm birth and low birth weight. We found weak evidence that particulate matter risk was higher for infants of mothers with lower educational attainment for preterm birth and low birth weight. Due to the small study numbers, we were unable to conclude whether effect modification is present for income, occupation, and area-level socio-economic status, and additional research is needed. Furthermore, adverse birth outcomes such as SGA and stillbirth need more study to understand potential environmental justice issues regarding the impact of particulate matter exposure during pregnancy on birth outcomes.

Keywords: Air pollution; birth outcomes; effect modification; environmental justice; particulate matter; race and ethnicity; socioeconomic status.

Fig. 1.

Flow chart of identified studies for systematic review. Notes. PM=particulate matter. SES=socio-economic status.

Figure 3.

Summary of scientific evidence of effect modification by maternal race and socio-economic status. Notes. RA: race/ethnicity, ED: education, IC: income, OC: occupation, SES: area-level integrated SES level, BW: low birth weight (dichotomous) and birth weight (continuous outcome), PTB: preterm birth, SGA: small gestational age. The strength of evidence was determined based on both the numbers of total studies and the study results of effect modification based on statistically significant associations between particulate matter exposure and birth outcomes (see Methods for more detail).