Infertility is a growing global public health concern, affecting roughly 15 % of reproductive-age couples worldwide (Zhou et al., 2021). In China, the prevalence of infertility have risen from 11.9 % in 2007 to 18 % in 2020 (Wang et al., 2024a). Ovarian reserve, defined as the quantity and quality of follicles in both ovaries, is a key indicator of female reproductive potential (Broekmans et al., 2010). Common indicators used to assess ovarian reserve include antral follicle count (AFC), anti-Müllerian hormone (AMH), and estradiol (E2) (Salemi et al., 2024; Practice Committee of the American Society for Reproductive Medicine, 2020). AFC reflects the available pool of small antral follicles, serving as a direct measure of ovarian reserve. AMH, a glycoprotein hormone secreted by granulosa cells of early developing follicles, also indicates the size of the remaining follicular pool. E2, a steroid sex hormone produced by ovarian follicles, is often combined with other biomarkers to predict for ovarian reserve due to menstrual cycle variation (Tal and Seifer, 2017; Findlay et al., 2015).

Prior studies have shown that genetic, environmental, and psychological factors all contribute to the decline in ovarian reserve (Hu et al., 2025; Huang et al., 2025; Han et al., 2024a). Among these, environmental exposures, particularly ambient particulate matter (PM), has been extensively studied (La Marca et al., 2020; Quraishi et al., 2019; Han et al., 2024b). Since the implementation of the “Blue Sky Defense Battle” (a national air pollution control campaign in China), concentrations of common air pollutants, including PM and sulfur dioxide have decreased excepted for ozone, with the annual concentration from 80.07 μg/m3 in 2016 to 96.04 μg/m3 in 2023 (Zhang et al., 2025). However, evidence regarding the impact of ambient ozone exposure on ovarian reserve remains limited and inconsistent. A study conducted in Wuhan involving 4544 women reported an association between exposure to ambient ozone and a decline in AMH (Liu et al., 2024). In contrast, other studies found no significant association between ozone exposure and AMH (Pang et al., 2023; Kim et al., 2021). Additionally, most existing studies have focused solely on AMH, neglecting other ovarian reserve biomarkers such as AFC. Since AFC provides a direct assessment of the number of small antral follicles, evaluating multiple biomarkers can allow for a more comprehensive and robust assessment of ovarian reserve.

Given the ongoing decline in female fertility and the rise in ambient ozone levels in China, it is imperative to estimate the association between ozone exposure and ovarian reserve. Therefore, we sought to evaluate the association between ambient ozone exposure and multiple ovarian reserve biomarkers, including AFC, AMH, and E2, among 2815 reproductive-age women in Sichuan, China. Additionally, we sought to identify critical exposure windows and vulnerable subpopulations.