The forward motility of sperm is usually greater than 32% under normal conditions, and the sum of forward and non-forward motile sperm >40%. Sperm motility is categorized into 3 grades according to the classification criteria in the fifth edition of the WHO manual: (1) Anterograde motility, which is defined as spermatozoa actively moving in a straight line or along a large circumference, regardless of their speed. (2) Non-forward motility, which refers to all other forms of non-forward motility of the spermatozoa, such as swimming in a small circle, with little tail power to drive the head to move, or with only tail wagging observed. (3) Inactivity, is the absence of sperm movement. The motility of sperm refers to the sum of forward-moving and non-forward-moving sperm, and the normal standard is >32% for forward-moving sperm and >40% for the sum of forward-moving and non-forward-moving sperm.