Exposure to fine particulate matter during pregnancy increases the risk of spontaneous preterm birth by 15% per interquartile range, according to a recent study. 

The retrospective cohort study of 409,037 live births in Southern California examined the relationship between fine particulate matter (PM_2.5) exposure during pregnancy and spontaneous preterm birth (sPTB). Researchers found that increased PM_2.5 exposure, particularly during the second trimester, was significantly associated with a higher risk of sPTB. 

For every interquartile range (IQR) increase in PM_2.5 (2.76 µg/m³), the adjusted odds ratio (aOR) for sPTB was 1.15 (95% confidence interval [CI], 1.12-1.18; P < .001). Among PM_2.5 constituents, black carbon had the strongest association (aOR per IQR [1.05 µg/m³], 1.15; 95% CI, 1.11-1.20), followed by nitrate (aOR per IQR [0.93 µg/m³], 1.09; 95% CI, 1.06-1.13) and sulfate (aOR per IQR [0.40 µg/m³], 1.06; 95% CI, 1.03-1.09).

Socioeconomic and environmental factors modified these associations. Participants without a college degree or with household incomes below the 50th percentile had a significantly higher risk (aOR 1.16 and 1.17, respectively). Limited green space exposure amplified risk (aOR 1.19; 95% CI, 1.15-1.23; P = .003), while extreme heat exposure showed the greatest risk modification (aOR 1.51; 95% CI, 1.42-1.59; P < .001). In contrast, areas with tree-dense green spaces were associated with reduced odds of sPTB.

The findings indicate that reducing PM_2.5 exposure and increasing urban green space may be associated with lower sPTB risks, particularly among subgroups facing socioeconomic and environmental disadvantages. 

Published in JAMA Network Open, this study has limitations, including potential exposure misclassification due to reliance on census tract-level PM_2.5 data without accounting for individual time-activity patterns or the limited availability of data on additional PM_2.5 elements and phenotypes of sPTB. While sensitivity analyses using alternative data sources supported the robustness of findings, future research with finer temporal and spatial resolution and expanded constituent analysis could enhance understanding of the mechanisms involved.

Full disclosures can be found in the published study.