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 (PM2.5) during pregnancy. However, the contribution of individual PM2.5 constituents risk remains unclear. This research investigated associations between prenatal exposure to PM2.5 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 PM2.5 constituents—including black carbon (BC), organic matter (OM), nitrate (NO3−), ammonium (NH4+), and sulfate (SO42−)—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 PM2.5 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 PM2.5 to the WHO recommended levels) yielded risk differences of −2.29 (BC), −3.70 (OM), −4.74 (NH4+), −5.00 (NO3−), and −2.11 (SO42−) per thousand births, corresponding to 312 (3.20%) to 740 (7.58%) preventable cases. Our results indicate that reductions in PM2.5 constituents, especially NO3− and NH4+, were associated with lower risks of PTB.