Timing Matters: Component-specific PM 2.5 Exposure Windows and Oocyte Development in Assisted Reproduction.

OBJECTIVE: Fine particulate matter (PM 2.5) may impair follicular development; however, the roles of its chemical components and their time-specific effects remain unclear. This study examined how PM 2.5 and its major components are related to oocyte-related outcomes among women undergoing assisted reproductive technology (ART) and identified critical exposure windows. METHODS: A total of 51,122 ART cycles were analyzed. Individual exposures to PM 2.5 and its components, sulfate (SO 4 2-), nitrate (NO 3 -), ammonium (NH 4 +), organic matter (OM), and black carbon (BC), were estimated for three periods: recent (0-3 months), distal (4-12 months), and cumulative (0-12 months). Associations between total, mature, and normally fertilized oocytes were assessed using negative binomial regression. Distributed lag non-linear models (DLNM) identified sensitive windows, and mixture models evaluated joint effects. RESULTS: Higher PM 2.5 and component exposures were consistently associated with poorer oocyte outcomes, with stronger effects for distal exposure. Two sensitive windows, 1 month and 6-11 months before retrieval, were identified. Mixture analyses indicated SO 4 2- and NH 4 + as the dominant contributors. CONCLUSION: Exposure to PM 2.5 showed component-specific and time-dependent reproductive toxicity. Both short- and long-term exposure may reduce oocyte quantity and quality, highlighting the importance of improving air quality to support female reproductive health and ART success.