Association between ambient fine particulate matter and preterm birth or term low birth weight: An updated systematic review and meta-analysis.

An increasing number of studies have been conducted to determine a possible linkage between maternal exposure to ambient fine particulate matter and effects on the developing human fetus that can lead to adverse birth outcomes, but, the present results are not consistent. A total of 23 studies published before July 2016 were collected and analyzed and the mean value of reported exposure to fine particulate matter (PM2.5) ranged from 1.82 to 22.11 We found a significantly increased risk of preterm birth with interquartile range increase in PM2.5 exposure throughout pregnancy (odds ratio (OR) = 1.03; 95% conditional independence (CI): 1.01-1.05). The pooled OR for the association between PM2.5 exposure, per interquartile range increment, and term low birth weight throughout pregnancy was 1.03 (95% CI: 1.02-1.03). The pooled ORs for the association between PM2.5 exposure per 10 increment, and term low birth weight and preterm birth were 1.05 (95% CI: 0.98-1.12) and 1.02 (95% CI: 0.93-1.12), respectively throughout pregnancy. There is a significant heterogeneity in most meta-analyses, except for pooled OR per interquartile range increase for term low birth weight throughout pregnancy. We here show that maternal exposure to fine particulate air pollution increases the risk of preterm birth and term low birth weight. However, the effect of exposure time needs to be further explored. In the future, prospective cohort studies and personal exposure measurements needs to be more widely utilized to better characterize the relationship between ambient fine particulate exposure and adverse birth outcomes.