A Sperm Diagram or semen analysis is used to determine whether a man might be infertile-unable to get a woman pregnant. The semen analysis has many parts and tests a lot of aspects of the semen and sperm. A semen analysis to determine fertility should be performed on a minimum of two samples at least seven days apart over a period of two to three months because some conditions can affect sperm levels.

A semen sample is characterized by:

• oligospermia when the number of spermatozoa is lower than normal (<20 million/ml)
• asthenospermia when the percentage of motile spermatozoa is low
• oligoasthenospermia when both the number and motility are lower than normal
• teratospermia when a high percentage of malformed spermatozoa is observed
• azoospermia when spermatozoa are completely absent.

The semen analysis also can be used to count sperm after a man has a vasectomy. If there are still a lot of sperm present in the semen, the man and his partner will have to take precautions so that his partner will not become pregnant. He will have to return for one or more sperm counts until the sperm are cleared from his sample(s).

The typical volume of semen collected is around one-half to one teaspoonful (2-6 milliliters) of fluid. Less semen would indicate fewer sperm, which would affect fertility. More semen indicates too much fluid, which would dilute the sperm, also impeding fertility.

Sperm concentration (also called sperm density) is measured in millions of sperm per milliliter of semen. Normal is greater than or equal to 20 million per milliliter (and more than 80 million sperm in one ejaculation). The fewer sperm a sample has, the less chance a man has of getting a woman pregnant. A man who has just had a vasectomy would want to have no sperm in his sample.

Motility is the percentage of moving sperm in a sample. The more slowly moving or immobile sperm in a sample, the less likely it is that a man could get a woman pregnant. The progression of the sperm is rated on a basis from zero (no motion) to 4 for sperm that move in a straight line with good speed. If less than half of the sperm are motile, a stain is used to identify the percentage of dead sperm. This is called a sperm viability test.

Morphology analysis is the study of the size, shape, and appearance of the sperm cells. The analysis evaluates the structure of 200 sperm, and any defects are noted. The more abnormal sperm that are present, the lower the likelihood of fertility.