Defining Infertility in Men

Male infertility is directly connected to the amount and quality of sperm a man produces. Some statistics suggest that 90 percent of male infertility is caused by poor sperm quality and low sperm counts. For the remaining 10 percent of infertile men, no known cause is detected. Obstruction is the largest cause of low sperm count with it being a contributing factor in 60 percent of cases according to one study. Poor sperm quality is caused by sperm abnormalities in approximately 30 percent to 40 percent of cases.

Percentages are just a guideline and there are areas called gray zones between the percentages. In these gray zones it can be difficult to define or determine male infertility.

What is Normal Sperm Count?

The number that's considered a normal sperm count varies from study to study. But it's generally thought that a man is fertile if he has a sperm count over 48 million per milliliter of semen. A man is considered infertile if the counts are below 13.5 million.

Sperm Movement

Sperm motility, meaning a sperms ability to move, is also an issue connected to male fertility. Sperm needs to be strong enough to move through the woman's cervix, uterus and reach the fallopian tubes. Not every single sperm a man ejaculates in his semen will be this strong, but for a man to fertile, it's generally thought that more than 63 percent of the sperm should be moving. A man who is considered less likely to conceive would have a sperm motility of less than 32 percent.

Sperm motility is considered poor if the sperm doesn't move in a straight line or is slow. Sluggish moving sperm could have genetic problems that make it impossible for them to penetrate the hard outer shell of an egg and fertilize it.

Sperm Shape

The shape and structure of the sperm (also called sperm morphology) is also important for a man's fertility. Once again, of the many sperm a man produces in a single ejaculation, not all will be the ideal shape. Researchers agree that more than 12 percent of the sperm should be normal in structure and shape for a man to be considered fertile. An infertile man will generally have fewer than nine percent normal shaped sperm.

A normal-shaped sperm should have a long tail and an oval head. Misshaped sperm can include a very large round head, a small pinpoint head, two heads, a tail with curls and kinks, a crooked head or a tapered head.

Sperm morphology can also affect sperm mobility.