Follicular-fluid neonicotinoid exposure and endometriosis: associations with reproductive outcomes and metabolic remodeling

Neonicotinoid insecticides (NEOs) are emerging environmental contaminants, but their presence and reproductive relevance in the human follicular microenvironment remain poorly understood. We quantified 16 NEOs and metabolites in follicular fluid from 174 infertile women undergoing assisted reproductive technology (ART), including 63 women with endometriosis and 111 controls. Associations with endometriosis and ART outcomes were assessed using single-analyte regression and mixture models. Untargeted metabolomics was performed in a nested subset of 40 women. NEOs were widely detected in follicular fluid, with N-desmethyl-acetamiprid (N-dm-ACE) showing the highest detection frequency. Each twofold increase in N-dm-ACE concentration was associated with higher odds of prevalent endometriosis (adjusted OR = 1.79, 95% CI: 1.38-2.32), and N-dm-ACE was consistently prioritized in mixture analyses. Several NEOs were also associated with adverse ART outcomes, including fewer mature oocytes, fewer two-pronuclear zygotes, and lower pregnancy odds, with stronger patterns among women with endometriosis. Metabolomic profiling identified 324 features differing between women with and without endometriosis at nominal P < 0.05, of which 54 remained significant after false discovery rate correction. Integrated exposure-metabolome analysis identified 47 features showing nominal associations with both N-dm-ACE and endometriosis. These findings identify cross-sectional associations between follicular-fluid NEO concentrations and existing endometriosis, alongside exploratory metabolic signatures involving lipid- and nucleotide-related features. Further longitudinal studies are needed to clarify their temporal and biological relevance.