Residential Exposure to PM2.5 Constituents and Fecundability in a Danish Preconception Cohort.

Background: Epidemiologic studies have demonstrated that ambient concentrations of particulate matter < 2.5 μm (PM_2.5) are associated with reduced fecundability, the per cycle probability of conception. The specific constituents driving this association are unknown.

Objectives: We examined the association between ambient concentrations of PM_2.5 constituents and fecundability in a Danish preconception cohort study.

Methods: During 2007-2018, we enrolled female pregnancy planners in an Internet-based preconception cohort study. We included the 5905 participants who had been trying to conceive for < 3 cycles at study enrollment. Participants completed a baseline questionnaire and follow-up questionnaires every 8 weeks to update pregnancy status. We geocoded time-varying residential addresses to estimate ambient concentrations of total PM_2.5 and the following PM_2.5 constituents: elemental carbon (EC), primary organic aerosol (POA), secondary organic aerosols (SOA), sulfate (SO₄ ^2-), ammonium (NH₄ ⁺), nitrate (NO₃ ^-), and sea salt. We averaged concentrations of each pollutant across each menstrual cycle at risk. We fit proportional probabilities regression models to estimate fecundability ratios (FR) and 95% confidence intervals (CI), adjusting for potential confounders and co-pollutants.

Results: Total PM_2.5 concentrations were associated with reduced fecundability (the FR for an IQR increase, corresponding to 3.2 μg/m³, was 0.93 [95% CI 0.87, 0.99]). The association was strongest for POA: the FR for an IQR increase, corresponding to 1.3 μg/m³, was 0.92 (95% CI 0.84, 1.01). The corresponding FRs for the remaining PM_2.5 constituents were 0.96 (95% CI 0.87, 1.05) for EC (IQR = 0.5 μg/m³), 0.98 (95% CI 0.91, 1.06) for SOA (IQR = 0.5), 0.97 (95% CI 0.92, 1.02) for SO₂ ^4- (IQR = 0.4), 0.95 (95% CI 0.91, 1.01) for NH₄ ⁺ (IQR = 0.5), 0.97 (95% CI 0.93, 1.01) for NO₃ ^- (IQR = 1.0), and 1.00 (95% CI 0.95, 1.06) for sea salt (IQR = 0.4).

Conclusions: In this Danish preconception cohort study, PM_2.5 constituents derived from biomass and transportation-related combustion may drive the association between PM_2.5 concentrations and fecundability.