Reduced human fecundity attributable to ambient fine particles in low- and middle-income countries.

Background: Exposure to ambient fine particulate matter (PM) has been associated with reduced human fecundity. However, the attributable burden has not been estimated for low- and middle-income countries (LMICs), where the exposure-response function between PM and the infertility rate has been insufficiently studied.

Objective: This study examined the associations between long-term exposure to PM and human fecundity indicators, namely the expected time to pregnancy (TTP) and 12-month infertility rate (IR), and then estimated PM-attributable burden of infertility in LMICs.

Methods: We analyzed 164,593 eligible women from 100 Demographic and Health Surveys conducted in 49 LMICs between 1999 and 2021. We assessed PM exposures during the 12 months before a pregnancy attempt using the global satellite-derived PM estimates produced by Atmospheric Composition Analysis Group (ACAG). First, we created a series of pseudo-populations with balanced covariates, given different levels of PM exposure, using a matching approach based on the generalized propensity score. For each pseudo-population, we used 2-stage generalized Gamma models to derive TTP or IR from the probability distribution of the questionnaire-based duration time for the pregnancy attempt before the interview. Second, we used spline regressions to generate nonlinear PM exposure-response functions for each of the two fecundity indicators. Finally, we applied the exposure-response functions to estimate number of infertile couples attributable to PM exposure in 118 LMICs.

Results: Based on the Gamma models, each 10 µg/m increment in PM exposure was associated with a TTP increase by 1.7 % (95 % confidence interval [CI]: -2.3 %-6.0 %) and an IR increase by 2.3 % (95 %CI: 0.6 %-3.9 %). The nonlinear exposure-response function suggested a robust effect of an increased IR for high-concentration PM exposure (>75 µg/m). Based on the PM-IR function, across the 118 LMICs, the number of infertile couples attributable to PM exposure exceeding 35 µg/m (the first-stage interim target recommended by the World Health Organization global air quality guidelines) was 0.66 million (95 %CI: 0.061-1.43), accounting for 2.25 % (95 %CI: 0.20 %-4.84 %) of all couples affected by infertility. Among the 0.66 million, 66.5 % were within the top 10 % high-exposure infertile couples, mainly from South Asia, East Asia, and West Africa.

Conclusion: PM contributes significantly to human infertility in places with high levels of air pollution. PM-pollution control is imperative to protect human fecundity in LMICs.