Sperm potency: For many men infertility is due to a low sperm count, which is generally associated with a high rate of sperm defects (size, shape and movement).
Testicular failure: Some men are found to have no sperm in their semen. This can be due to a failure to ejaculate or a failure of the testes to produce sperm. The testes may have been damaged due to a poor blood supply, injury or even a case of adult mumps. Other causes include hormonal imbalances and genetic defects.
Vas deferens blockage: Damage as a result of infections can prevent the sperm from traversing the vas deferens. Occasionally, the ejaculate of some men is diverted into the bladder. This is known as “retrograde ejaculation”.
Sperm antibodies: A small group of men actually produce antibodies against their own sperm.