There are a wide number of reasons for male infertility. Some are caused by physical problems that prevent the sperm from being ejaculated normally in semen. Others affect the quality and production of the sperm itself.
Blockages, birth defects, or physical damage. In some cases, men are born with blockages in parts of the testicle or other abnormalities that prevent sperm from getting into the semen. Physical trauma to the testicles, prostate, and urethra can also result in fertility problems. Surgery can sometimes correct the problem.
Retrograde ejaculation. In this disorder, semen doesn't come out of the penis during ejaculation, but instead enters the bladder. It can be caused by diabetes, certain medications, and surgery to the bladder, prostate, or urethra.
Genetic diseases. Although it's rare, genetic illnesses such as cystic fibrosis or chromosomal disorders can cause infertility.
Autoimmune problems. In some cases, the immune system can mistakenly target sperm cells and treat them as if they were a foreign virus. The sperm can become damaged as a result.
Hormonal problems. Certain hormonal imbalances -- in the pituitary and thyroid glands, for instance -- can cause infertility. Your doctor may suggest treatment with medication.
Varicoceles. Varicoceles are enlarged varicose veins that develop in the scrotum and prevent blood from flowing properly. Varicoceles are found in 15% of all men and in up to 40% of men being evaluated for infertility. Although they may be a factor in male infertility, recent studies question whether surgery to correct varicoceles has any beneficial effect.