Relationship Between Sperm DNA Fragmentation and Composite Morphological Indices: A Multivariable Analysis

Background and Objectives: Although conventional semen analysis remains central in male infertility evaluation, the biological relationship between sperm morphology and genomic integrity remains incompletely defined. Sperm DNA fragmentation (SDF) has emerged as a clinically relevant marker of genomic instability; however, its relationship with composite morphological indices of spermatogenic dysfunction remains debated. This study aimed to evaluate the relationship between sperm DNA fragmentation assessed in the post-swim-up fraction and composite sperm morphological indices derived from raw semen, using a multivariable analytical framework that accounts for conventional semen parameters. Materials and Methods: This observational study included 183 semen samples from men undergoing fertility evaluation. SDF was assessed using a sperm chromatin dispersion (SCD)-based assay in the post-swim-up fraction. Sperm morphology was evaluated in raw semen according to World Health Organization criteria, and composite morphological indices, namely the Teratozoospermia Index (TZI), Sperm Deformity Index (SDI), and Multiple Anomalies Index (MAI), were calculated. Associations were examined using Spearman correlation and multivariable linear regression models adjusted for sperm concentration and progressive motility. Exploratory distributional analyses were performed across clinically defined SDF categories. Results: Bivariate analyses demonstrated weak, non-significant positive correlations between SDF and all composite morphological indices. None of the morphological indices independently predicted SDF after adjustment for sperm concentration and progressive motility in multivariable regression models. In contrast, sperm concentration showed a consistent inverse association with SDF. Distributional analyses revealed substantial overlap between morphological severity and SDF categories, indicating heterogeneity in the co-occurrence of structural abnormalities and DNA fragmentation at the individual sample level. Conclusions: Composite sperm morphological indices were not independently associated with sperm DNA fragmentation after adjusting for quantitative semen parameters in the present analytical framework. These findings suggest that structural abnormalities and genomic instability may capture complementary aspects of male infertility rather than representing interchangeable markers. SDF assessment may therefore provide complementary diagnostic information beyond morphology-based evaluation, particularly in assisted reproductive contexts.