The “male factor” contributes to infertility around half the time, and about one third of the time, it's the main cause of infertility. Most often, the problem lies in the process of either making or moving the sperm.

Any of the following can cause a man to have a low sperm count or abnormal sperm:

• Varicocele — an abnormal collection of bulging veins above the testicle; they’re the most common cause of correctable male infertility, accounting for 38% of cases.
• Undescended testicle.
• Infections in the testicle (orchitis), the prostate (prostatitis), or elsewhere in the body that causes a fever.
• Chemotherapy for cancer.
• Medicines such as anabolic steroids or anti-seizure medicines.
• Genetic abnormalities.
• Hormone problems.

In some cases, these problems can be reversed, but other times they can’t. An evaluation by a physician is the only way to sort it out.

Sometimes, making sperm isn't the problem. The problem is getting the sperm where they need to go. Men with this type of male infertility have normal sperm in the testicles. But the sperm in the semen are either abnormal, very low in number, or not there at all. Causes of this kind of infertility include:

• Retrograde ejaculation. In this condition, semen ejaculates backwards into the bladder instead of out the penis. Usually previous surgery is the cause.
• Absence of the main sperm pipeline known as the vas deferens. This condition is a genetic problem.
• Obstruction. An obstruction can occur anywhere in the plumbing between the testicles and the penis.
• Anti-sperm antibodies. Antibodies can abnormally attack a man's own sperm on their way to the egg.

Up to 25% of infertile men have idiopathic infertility. That means they have abnormal or low sperm counts for no identifiable reason.

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