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Sperm morphology - does it have a normal head/tail?
Sperm concentration - are there enough sperm within the ejaculate?
Capacitation - can the sperm properly undergo this 'activation process' and become capable of fertilisation? Non-capacitated sperm can't fertilise eggs.
Progressive Motility - can the sperm swim properly and cover the distance?
Hyperactivated Motility - can the sperm wriggle intensively to escape sticky parts of the female reproductive tract eg mucus plug at cervix, lots of mucus along the way, penetrate egg?
Acrosome reaction - can the sperm produce enzymes to dissolve/digest the tough walls (known as zona pellucida) surrounding the egg?
Survival - can the sperm just....survive all the way?
Only when the sperm possesses all these capabilities then will it have a chance to be considered at fertilisation.
Increasingly folks have realised that there's another checkpoint that the sperm must bypass to trigger fertilisation:
Plc-zeta (think of it as like an engagement ring) - does the sperm have this protein and able to pass this protein to an egg once sperm has properly penetrated the egg? (The egg will not be fertilised if sperm cells do not present this 'engagement ring' to egg cells even if the sperm has physically entered the egg).
So it's really quite an arduous journey a sperm cell has to make within the female reproductive tract, making all of us miracles of nature.