Male factor infertility can be caused by a number of different characteristics of the sperm. To check for these characteristics, a semen analysis is carried out, during which a sample of semen is obtained and examined under the microscope. The four most basic characteristics evaluated are sperm count, sperm motility, sperm morphology, and semen volume.

Sperm count concerns the number of sperm present in a semen sample. The normal number of sperm present in just one milliliter (ml) of semen is over 20 million. A man with only 5-20 million sperm per ml of semen is considered subfertile, a man with less than five million sperm per ml of semen is considered infertile.

Sperm motility is important because better swimmers indicate a higher degree of fertility, as does longer duration of survival. Sperm are usually capable of fertilization for up to 48 hours after ejaculation.

Sperm morphology or...