Grade A sperm is the most active sperm. Spermatozoa are classified into four classes according to their motility, which are denoted by the letters A, B, C and D. Class A sperm represent spermatozoa with fast linear forward motion, the highest sperm motility and the best quality, Class B sperm refer to spermatozoa with slow forward motion, Class C sperm usually refer to spermatozoa with in situ motion, and Class D sperm usually refer to spermatozoa with no D sperm are usually non-motile sperm. The percentage of A-grade sperm plus B-grade sperm to the total sperm count is ≥32%, which usually indicates normal sperm viability, and less than this value indicates the presence of weak sperm.