Semen quality is basically evaluated according to the following parameters: concentration (number of sperm detected per 1 ml of semen), motility (sperm movement) and morphology (percentage of normal sperm).
Sperm quality may show temporary or permanent damage. A high fever or recent exposure to toxic substances can also impair sperm quality, as can radiological applications performed near the testicles. Male age may also partially affect sperm quality, as well as excessive alcohol use and/or heavy smoking.
Levels of semen quality fluctuate in a yearly basis and may also vary in each ejaculation. According to the WHO recommendations, in order to evaluate most accurately the variation of semen quality, it is recommended to examine two semen samples collected at a time distance of 1 to 2.5 months.