Problems related to STDs affects male reproductive system. STD can also affect male fertility. Chlamydia, when left untreated, may spread to the testicles from the urethra, causing permanent sterility and disability. Pelvi inflammatory disease is common STD that affects fertility. A low sperm count and low sperm motility are indicators of this condition. Also, elevated FSH levels and other hormonal problems are indicative of testicular damage. Some STDs like gonorrhea and chlamydia can cause infertility by blocking the epididimis or tubes.