Ch21

• 2 to 7 days of sexual abstinence before collection.
• Two separate samples at least 7 days apart.
• The duration of abstinence should be constant, if possible, because each additional day can add as much as 25% in sperm concentration

• 
• Viablility - 58% live spermatozoa

• A more specified measure is motility grade, where the motility of sperm are divided into four different grades:
• Grade a: Sperm with progressive motility. These are the strongest and swim fast in a straight line. Sometimes it is also denoted motility IV.
• Grade b: (non-linear motility): These also move forward but tend to travel in a curved or crooked motion. Sometimes also denoted motility III.
• Grade c: These have non-progressive motility because they do not move forward despite the fact that they move their tails. Sometimes also denoted motility II.
• Grade d: These are immotile and fail to move at all. Sometimes also denoted motility I.

When semen volume is low, a search must be made for spermatozoa in urine after ejaculation. Absence of spermatozoa and immature germ cells in semen smears suggest complete seminal duct obstruction.