Elevated sperm DNA fragmentation is associated with embryonic developmental attrition after fertilization in conventional IVF cycles

Background The influence of sperm DNA fragmentation on conventional in vitro fertilization (IVF) outcomes remains controversial, particularly regarding whether its embryological relevance is expressed during fertilization or subsequent embryo development. This study aimed to evaluate the association between sperm DNA fragmentation index (DFI) and stage-specific embryological transition outcomes in a retrospective cohort of first eligible conventional IVF cycles. Methods This retrospective cohort study included 1,423 first eligible conventional IVF cycles selected from fresh oocyte-retrieval treatment cycles recorded between August 2021 and December 2025. Cycles involving intracytoplasmic sperm injection, rescue intracytoplasmic sperm injection, or mixed fertilization procedures were excluded. Sperm DFI was categorized using a primary threshold of 20%, with cycles classified as lower DFI (≤20%) or elevated DFI (>20%). Embryological development was assessed using stage-specific transition outcomes, including oocyte-to- two-pronuclear (2 P N) formation, 2 P N-to-day-3 good-quality embryo formation, blastocyst formation among embryos cultured for blastocyst development, and blastocyst-to-good-quality blastocyst formation. Binomial regression models were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Multivariable models were adjusted for female age, male age, female body mass index, and basal follicle-stimulating hormone. Additional analyses examined clinically interpretable DFI categories and alternative DFI thresholds. Results Among the 1,423 cycles, 1,218 were classified as lower DFI and 205 as elevated DFI. Elevated DFI was not associated with the oocyte-to-2PN transition after adjustment (63.7% vs. 62.3%; adjusted OR, 0.96; 95% CI, 0.84–1.10; P = 0.523). In contrast, elevated DFI was associated with a lower probability of 2 P N-to-day-3 good-quality embryo formation (34.5% vs. 29.4%; adjusted OR, 0.71; 95% CI, 0.57–0.87; P = 0.001). Elevated DFI was also associated with reduced blastocyst formation among embryos cultured for blastocyst development (57.3% vs. 50.4%; adjusted OR, 0.80; 95% CI, 0.66–0.96; P = 0.018). Good-quality blastocyst formation among formed blastocysts was 34.4% in the lower-DFI group and 30.8% in the elevated-DFI group (adjusted OR, 0.87; 95% CI, 0.68–1.11; P = 0.267). Analyses using clinically interpretable DFI categories and alternative thresholds showed that the association was most consistently observed for post-fertilization developmental outcomes rather than normal fertilization. Conclusion In this retrospective cohort of first eligible conventional IVF cycles, elevated sperm DFI was not independently associated with normal fertilization but was associated with modestly reduced post-fertilization embryological development, particularly 2 P N-to-day-3 good-quality embryo formation and blastocyst formation among embryos cultured for blastocyst development. These findings support a stage-specific developmental framework for evaluating the embryological relevance of paternal DNA integrity in conventional IVF, while suggesting that sperm DFI should not be interpreted as a stand-alone marker of fertilization potential.