Objective assessment of transition hyperactivated motility in 10-μm chambers: a functional predictor of sperm recovery in assisted reproduction

Background Conventional sperm motility analysis often fails to capture the dynamic physiological changes associated with fertilization. The identification of a transition hyperactivated (TH) phenotype, characterized by high vigor while preserving linearity, may provide additional information on ejaculate functional competence beyond standard semen parameters. Objective To establish an objective method for detecting TH motility using computer-assisted sperm analysis (CASA) with 10-μm chambers and to evaluate its clinical predictive value in comparison with pharmacological induction. Materials and methods The Sperm Class Analyzer (SCA) system (Microptic SL) was validated using the following kinematic thresholds: curvilinear velocity (VCL) > 35 μm/s, linearity (LIN) > 50%, and amplitude of lateral head displacement (ALH) > 2.5 μm. Semen samples from fertile men ( n = 27) and men consulting for infertility ( n = 229) were analyzed under different conditions. TH motility was assessed in ejaculated semen (THE), after swim-up (THS), and after overnight incubation (THO). The non-genomic effects of thyroxine (T4, 0.002 μg/mL) on TH induction and on the number of total recovered spermatozoa (NTRS) were also evaluated. Results Significant differences were observed among the analyzed conditions (Kruskal–Wallis test with Conover post-hoc analysis, p < 0.001). Fertile men showed no significant difference between THE and THO, whereas significant differences were observed in men consulting for infertility. THE was significantly higher in fertile men than in men with infertility [median (interquartile range, IQR): 8.2% (4.9–14.8) vs. 4.9% (2.7–9.0); p < 0.001]. THE values above the upper quartile of patients with infertility (> 9%) correlated with NTRS (Spearman’s rs = 0.779, p = 0.0004). In paired samples, T4 treatment significantly increased NTRS [median (IQR): 4.4 × 10 6 (3.6–9.2) vs. 10.7 × 10 6 (6.1–16.7); p = 0.00075], enabling samples to reach the threshold for intrauterine insemination. Conclusion Transition hyperactivated motility represents a novel and objective functional biomarker of sperm kinematic competence beyond conventional semen parameters. Measurement of THE in 10-μm chambers provides a robust analytical approach for functional sperm assessment. Combined with T4 induction, this strategy may offer clinically relevant information on sperm functional status. Prospective studies including pregnancy outcomes are needed to determine its predictive value for clinical fertility and assisted reproduction.