Ambient air pollutant mixtures in relation to sonographic endometrial receptivity parameters during the peri-implantation window: a clinic-based observational study.

Although air pollution has been linked to adverse reproductive outcomes, its direct effect on endometrial receptivity-a critical factor for embryo implantation-remains unclear at the population level. This study aimed to evaluate the associations of exposure to a mixture of six ambient air pollutants (PM2.5, PM10, CO, NO2, SO2, O3) with sonographic endometrial receptivity parameters (thickness and volume). This clinic recruited observational study included 1,349 women from 14 cities in Liaoning Province, China. Monthly average pollutant concentrations before ultrasound assessment were derived from a high-resolution dataset. Quantile g-computation and Bayesian Kernel Machine Regression models were applied to assess joint effects. Both models consistently showed that exposure to the pollutant mixture was inversely associated with endometrial volume and thickness. A simultaneous one-quartile increase in the pollutant mixture was associated with a 0.5 mm reduction in endometrial thickness and a 0.28 ml reduction in volume. In mixture analyses, CO and O3 exhibited relatively stronger statistical contributions to these adverse associations. This study indicates that exposure to ambient air pollutant mixtures is associated with reduced sonographic markers of endometrial receptivity, with CO and O3 showing relatively stronger statistical contributions.