Exploratory Interim Analysis of Serial Plasma and Single-Follicle Follicular Fluid Oxidation–Reduction Potential During Fertility Treatment

Background/Objectives: This exploratory interim analysis examined associations between serial plasma oxidation–reduction potential (ORP) and single-follicle follicular-fluid (FF) ORP during fertility treatment. Between-visit measurements and cycle-level outcomes were also described. Methods: In 31 cycles from 29 women, plasma was sampled prospectively at cycle day 2 (D2), D6, and pre-trigger, and FF from one follicle at retrieval. Fresh samples were measured in duplicate (MiOXSYS); only means were available. All analyses were post hoc and used Spearman correlations, an intraclass correlation coefficient (ICC), and mixed models with within-family adjustment. Results: Plasma–FF correlations were 0.580 at D2 (n = 25; 95% confidence interval [CI], 0.178–0.839), 0.715 at D6 (n = 23; CI, 0.350–0.924), and 0.866 pre-trigger (n = 23; CI, 0.679–0.941). All Holm-adjusted p values were ≤0.0027. In 21 women with complete profiles, between-visit correlations were 0.703–0.856 (ICC, 0.788; CI, 0.617–0.872). The mixed-model pre-trigger minus D6 difference was 6.6 mV (CI, 0.6–12.6; Holm-adjusted p = 0.0939). No visit contrast or main ORP–outcome association met its adjusted threshold. Conclusions: Plasma and FF ORP were associated in this small interim cohort. Neither biological stability nor a true temporal change was established, and assay precision, agreement, and prognostic value remain unknown. Clinical application is not supported.