Associations of ambient air pollution exposure to fine particulate matter and its chemical constituents before and during pregnancy with the risk of full-term small for gestational age: a retrospective cohort study.

Objective: In the current study, we explored the associations between exposure to fine particulate matter (PM_2.5) constituents and full-term small for gestational age (SGA) in different periods.

Methods: We included 155,897 participants, and matched the exposure concentrations of PM_2.5 and its constituents [sulfate (SO₄^2-), nitrate (NO₃^-), ammonium (NH₄⁺), organic matter (OM), and black carbon (BC)] according to participants' geographical location. To explore the associations of prenatal exposure to PM_2.5 and its constituents with the risk of full-term SGA, we used logistic regression, restricted cubic spline regression (RCS) and quartile g-computation (QGCOMP).

Results: We found that individual exposure to PM_2.5 and its constituents was positively associated with the risk of full-term SGA (P < 0.05), whether in the year before pregnancy or the entire pregnancy. These associations were more pronounced in the second trimester. We found that the risk of full-term SGA was positively and linearly related to the concentrations of PM_2.5 and its constituents (P_overall < 0.05, P_nonlinear > 0.05). The associations of PM_2.5 and its constituents with full-term SGA were stronger in multiparous mothers. Moreover, full-term SGA was associated with exposure to mixtures of SO₄^2-, NO₃^-, NH₄⁺, OM, and BC before pregnancy and in the second and third trimester. Among these, BC was positively associated with full-term SGA at each of the aforementioned stages.

Conclusions: The risk of full-term SGA was positively and linearly related to concentrations of PM_2.5 and its constituents, and these associations were more pronounced in the second trimester. BC was the most hazardous constituent of PM_2.5 that was associated with full-term SGA.