Sperm DNA integrity is crucial for fertilization and development of healthy offspring. The spermatozoon undergoes extensive molecular remodeling of its nucleus during later phases of spermatogenesis, which imparts compaction and protects the genetic content. Testicular (defective maturation and abortive apoptosis) and post-testicular (oxidative stress) mechanisms are implicated in the etiology of sperm DNA fragmentation (SDF), which affects both natural and assisted reproduction. Several clinical and environmental factors are known to negatively impact sperm DNA integrity. An increasing number of reports emphasizes the direct relationship between sperm DNA damage and male infertility. Currently, several assays are available to assess sperm DNA damage, however, routine assessment of SDF in clinical practice is not recommended by professional organizations. This article provides an overview of SDF types, origin and comparative analysis of various SDF assays while primarily focusing on the clinical indications of SDF testing. Importantly, we report four clinical cases where SDF testing had played a significant role in improving fertility outcome. In light of these clinical case reports and recent scientific evidence, this review provides expert recommendations on SDF testing and examines the advantages and drawbacks of the clinical utility of SDF testing using Strength-Weaknesses-Opportunities-Threats (SWOT) analysis.

Several cellular insults can result in sperm DNA fragmentation either on one or both DNA strands. Oxidative damage, premature interruption of the apoptotic process and defects in DNA compaction during spermatogenesis are the main mechanisms that cause DNA breaks in sperm. The two-tailed Comet assay is the only technique that can differentiate single- (SSBs) from double- (DSBs) strand DNA breaks. Increased levels of the phosphorylated isoform of the H2AX histone are directly correlated with DSBs and proposed as a molecular biomarker of DSBs. We have carried out a narrative review on the etiologies associated with SSBs and DSBs in sperm DNA, their association with reproductive outcomes and the mechanisms involved in their repair. Evidence suggests a stronger negative impact of DSBs on reproductive outcomes (fertilization, implantation, miscarriage, pregnancy, and live birth rates) than SSBs, which can be partially overcome by using intracytoplasmic sperm injection (ICSI). In sperm, SSBs are irreversible, whereas DSBs can be repaired by homologous recombination, non-homologous end joining (NHEJ) and alternative NHEJ pathways. Although few studies have been published, further research is warranted to provide a better understanding of the differential effects of sperm SSBs and DSBs on reproductive outcomes as well as the prognostic relevance of DNA breaks discrimination in clinical practice.

Infertility is defined as the inability to conceive after 12 months of regular, unprotected intercourse (Sabanegh & Agarwal, 2010). Although 60%-75% of couples conceive within 6 months, and 90% within 12 months (Spira, 1986), approximately 48.5 million couples worldwide are considered infertile within this definition (Agarwal et al., 2019; Sharlip et al., 2002). Male factor infertility affects up to 50% of couple infertility and is solely responsible for 20% of overall infertility (Thonneau et al., 1991). In recent decades, the incidence of male factor infertility has increased (Turner et al., 2020; Zandieh et al., 2018). Semen analysis is considered as the cornerstone of the male fertility evaluation. This analysis provides information into the possible extent and severity of infertility problems, and aids in diagnosis and clinical management. Based on several population studies, the World Health Organization (WHO) provided updated sampling and laboratory guidelines with clinical thresholds to evaluate male reproductive potential through semen analysis (Mayorga-Torres, Camargo, Cadavid, du Plessis, & Cardona Maya, 2017). However, there remain several limitations associated with the conventional semen analysis in the assessment of male infertility (Majzoub, Agarwal, & Esteves, 2019). These limitations have led to the development of advanced sperm function and seminal fluid quality assessments, such as oxidative stress and sperm DNA fragmentation (SDF), that may better guide diagnostics, management and the prediction of male fertility outcomes (Esteves, Sharma, Gosálvez, & Agarwal, 2014). Spermatozoa are highly differentiated cells, which are made up of a head, mid piece and tail. The head of the spermatozoa contains the haploid genome that is transmitted into the oocyte after successful fertilization. The integrity and composition of the sperm DNA is different from that of somatic cells and critical for its fusion with the maternal genome (Conwell, Vilfan, & Hud, 2003). Adequate sperm DNA integrity is critical for successful fertilization, embryo development, implantation and establishment of pregnancy as it contributes towards 50% of the embryonic genome (Baskaran et al., 2019; Braude, Bolton, & Moore, 1988). Sperm DNA integrity is therefore considered as an important marker of fertility potential of spermatozoa (Cho & Agarwal, 2018).