Sperm Basics

In humans, fertilization depends on sperm that are properly shaped, or possess good morphology, as it’s clinically called, and are able to move rapidly toward the egg, a characteristic known clinically as having good motility.

While fertility has been traditionally perceived as largely a female problem, it’s important to remember that male infertility is involved in approximately 40 percent of infertile cases, according to the National Institutes of Health. About one-half of these men experience irreversible infertility and cannot father children, while others suffer a treatable medical condition.

Sperm production

Sperm development is called spermatogenesis. Although controlled by the body’s endocrine (hormonal) system, sperm development occurs in the ducts of the testes, with each production cycle consisting of six stages and requiring about 16 days.

Following development, sperm can swim to a female egg due to energy-generating parts of each cell called mitochondria, which power the sperm’s tail (flagellum) once inside the vagina.

Sperm by the numbers

Sperm count or concentration refers to the number of sperm cells per milliliter of semen. Men with 10 million or fewer sperm per milliliter are considered subfertile. Approximately 20 million or higher is considered average; 40 million sperm or higher per milliliter indicates increased fertility.

The diagnosis of oligospermia means there is a very low sperm count. Men diagnosed with azoospermia have no sperm in their semen. Often, there are no symptoms for this disorder, and men with this condition may even have a normal ejaculation process.

Sperm are carried in semen, in which normal volume ranges from 2 to 5 milliliters – about one-fourteenth to one-sixth of a fluid ounce.

Sperm motility is graded by the number and quality of the sperm movement, ranging in decreasing order from rapid progressive, slow progressive, non-progressive and immotile. Normal motility is when at least one-half of the sperm demonstrate rapid or slow progressive movement immediately after the sample liquefies and that movement is sustained for at least three hours.

Sperm vitality determines the number of living sperm in a sample. At least 50 percent of ejaculated sperm should be alive.

Sperm morphology is an assessment of the physical appearance of individual sperm, notably the head and tail characteristics. At least 30 percent of the sperm should be normal.

Azoospermia