Asthenozoospermia (or "asthenospermia") is the medical term for reduced sperm motility.
It decreases the sperm quality and is therefore one of the major causes of infertility or reduced fertility in men.
While the commonest cause of male infertility is a low sperm count ( the technical term for this is oligospermia), some men are infertile because of poor sperm motility. Normally, at least 50% of sperm should be motile; and this should be good quality progressive motility. This condition is called asthenospermiaor asthenozoospermia ( astheno = weak).
While many men with a low sperm count will also have poor sperm motility ( the two often co-exist, and this is called oligoasthenospermia), some men will have a normal sperm count, but very poor sperm motility.
Sperm motility ( whether the sperm are moving well or not ) can only be assessed when a semen analysis is performed in the laboratory . Sperm motility is the ability to move. Sperm are of two types - those which swim, and those which don't. Remember that only those sperm which move forward fast are able to swim up to the egg and fertilise it - the others are of little use.
Motility is graded from a to d, according to the World Health Organisation ( WHO) Manual criteria , as follows.
- Grade a ( fast progressive) sperm are those which swim forward fast in a straight line - like guided missiles.
- Grade b (slow progressive) sperm swim forward, but either in a curved or crooked line, or slowly (slow linear or non linear motility) .
- Grade c ( nonprogressive) sperm move their tails, but do not move forward ( local motility only).
- Grade d ( immotile ) sperm do not move at all .
Sperm of grade c and d are considered poor. Other laboratories grade sperm from a range of I to IV - and you need to ask your doctor what the grade refers to.