Associations of Gestational Exposure to Fine Particulate Matter Constituents with Preterm Birth: A Birth Cohort-Based Hypothetical Intervention Study

Preterm birth (PTB) has been increasingly linked to maternal exposure to fine particulate matter (PM_2.5) during pregnancy. However, the contribution of individual PM_2.5 constituents risk remains unclear. This research investigated associations between prenatal exposure to PM_2.5 constituents and PTB risk using a hypothetical intervention approach. A birth cohort of 148,068 mother-child pairs from Foshan, China was constructed from health records. Maternal exposure to PM_2.5 constituents-including black carbon (BC), organic matter (OM), nitrate (NO₃<b>^-</b>), ammonium (NH₄⁺), and sulfate (SO₄^2-)-was estimated based on satellite-derived spatial and temporal modeling. Parametric G-computation and distributed lag nonlinear models were used to estimate the cumulative risks of PTB under hypothetical reductions of PM_2.5 constituents during pregnancy. Potential benefits (preventable PTB cases) were also estimated. Among the cohort, 9757 (6.59%) PTBs were observed. Hypothetical reductions in all five constituents during pregnancy were associated with decreased cumulative risks of birth at week 36 (i.e., the threshold for PTB). For instance, a 40% reduction (reducing PM_2.5 to the WHO recommended levels) yielded risk differences of -2.29 (BC), -3.70 (OM), -4.74 (NH₄⁺), -5.00 (NO₃<b>^-</b>), and -2.11 (SO₄^2-) per thousand births, corresponding to 312 (3.20%) to 740 (7.58%) preventable cases. Our results indicate that reductions in PM_2.5 constituents, especially NO₃<b>^-</b> and NH₄⁺, were associated with lower risks of PTB.