" Effects of subclinical hypothyroidism on sperm quality parameter: A Systematic Review and Meta-Analysis." Running title: Meta-analysis of the Association between hypothyroidism and sperm quality parameter.

Introduction: Thyroid hormones affect the testes in different ways and various cell types, including Leydig, Sertoli and germ cells. Deficiency of thyroid hormones leads to alterations in testicular function, including abnormalities of seminal fluid. This systematic review with meta-analysis aimed to compare hypothyroidism and semen quality parameters such as sperm count, motility, and morphology. Materials and Methods: literature search was performed to identify eligible studies in the PubMed, Scopus, Embase, and Web of Science databases without restriction by region or language. A total of ۷ studies that met the eligibility criteria, and the collected data were analyzed using Comprehensive Meta-Analysis V۳ software for meta-analysis. Results: Finally, ۶ studies with a total of ۳۴۹۷ participants were identified. Cases of subclinical hypothyroidism had statistically significant decreases in total sperm count (SMD: -۰.۷۵, ۹۵% CI: -۱.۲۹ to -۰.۲۱), normal sperm morphology (SMD: -۰.۹۹, ۹۵% CI: -۲.۱۲ to -۰.۱۲), and progressive sperm motility (SMD: -۱.۵۶, ۹۵% CI: -۲.۷۸ to -۰.۳۴) compared with control groups. Conclusion: Thus, scientific evidence suggests that semen quality parameters are altered in Hypothyroidism patients compared to healthy controls. Therefore, despite of other factors, hypothyroidism may play an essential role in changing spermatogenesis and the development of infertility in men.