Varicoceles appear to cause male infertility by

The incidence of varicoceles in the general population is about 15%, but 40% of males with infertility are found to have varicoceles. Because of the anatomy and physiology, varicoceles are more likely to occur on the left side. There is no correlation between the size of the varix and prognosis for fertility. The characteristic stress pattern seen with varicoceles is decreased number of sperm, decreased motility, and increased abnormal forms. How the varicocele causes abnormal semen quality, and the relationship between varicocele, semen abnormalities, and male infertility (especially when semen quality appears normal) is unclear.