Sperm DNA Fragmentation

Sperm DNA integrity is critical for normal fertilization and early embryo development. High levels of DNA strand breaks — measured by the DNA fragmentation index (DFI) — are associated with reduced fertilization rates, poorer blastocyst development, higher miscarriage rates, and failure of recurrent IUI cycles, even when standard semen parameters appear normal.

Testing methods include TUNEL, SCSA (sperm chromatin structure assay), and Comet assay. A DFI above 15–25% (threshold varies by lab and assay) is considered elevated. Contributing factors include varicocele, oxidative stress, infection, smoking, and heat exposure. Treatment may include antioxidant supplementation, varicocele repair, or using testicular sperm (TESE) for ICSI, which typically has lower fragmentation than ejaculated sperm.