Different Proportions of Round-Headed Spermatozoa: Impacts on Sperm Function and IVF/ICSI Outcomes.

BACKGROUND: Although complete globozoospermia is well characterized, it is clinically rare. Partial globozoospermia is more prevalent, yet the impact of varying round-headed sperm ratios on disease severity remains unclear. Notably, even low proportions often signal compromised semen quality and spermatogenic dysfunction. This study investigates the impact of these proportions on sperm function and ART outcomes to provide evidence for individualized clinical management. METHODS: This was a retrospective case-control study. After balancing baseline characteristics by propensity score matching (PSM), 728 subjects were included in both the round-headed sperm group (proportion ≥ 5%) and the control group. A machine learning-based automatic sperm morphology analysis system was used to quantify the proportion of round-headed sperm and their head parameters. Sperm function indicators (DNA integrity, acrosome function, mitochondrial membrane potential) were detected, and 166 couples from the round-headed sperm group who received IVF/ICSI were included for reproductive outcome analysis. RESULTS: After PSM, the round-headed sperm group showed significantly lower normal morphology rate, sperm kinematic parameters, nucleoprotein maturation, acrosome integrity, and acrosin activity compared with the control group. The sperm DNA fragmentation index (DFI) and high DNA stainability (HDS) were higher in the round-headed sperm group (p < 0.001). ROC curve analysis based on clinical pregnancy outcomes determined that the cut-off value for the proportion of round-headed sperm is 7.2%. The high-proportion group (> 7.2%) exhibited significantly lower IVF fertilization rate and high-quality embryo rate than the low-proportion group (≤ 7.2%) (p < 0.01). In ICSI cycles, the high-proportion group had significantly lower high-quality embryo rate (48.48% vs. 40.33%, p = 0.016), clinical pregnancy rate (58.82% vs. 41.43%, p = 0.048), and live birth rate (50.98% vs. 32.86%, p = 0.028) than the low-proportion group. CONCLUSIONS: The proportion of round-headed sperm can serve as an objective predictor for sperm function and outcomes before assisted reproductive technology treatment.