Sperm Motility refers to the ability of sperm to move. The sperm need to be able to move in a co-ordinated manner, and in a forward direction if fertilization is to take place.
Sperm Motility is measured by performing a Semen Analysis.
Sperm Motility in the semen sample is described as either Progressive Motility or Non-Progressive Motility. Progressive Motility refers to the forward movement of the sperm in a straight line, or movement of the sperm in large circles. Non Progressive Motility refers to the movement of the sperm either in circles, or not moving in a straight line. Total Motility is then the sum of the Progressive Motility and the Non-Progressive Motility.
According to the WHO, in healthy men, the normal Total Motility is 42%, meaning at least 42% of the sperm should at very least, be moving, even if they are moving in small circles. The Progressive Motility needs to be at least 30%, meaning that at least 30% of the sperm need to be moving forward, in a straight line, or in large circles. Anything less than that is considered Low Sperm Motility. Low Sperm Motility is referred to as asthenospermia or asthenozoospermia.
Low Sperm Motility is one of the causes of male infertility, and can result in getting pregnant naturally, more difficult, because if the sperm is unable to swim towards the egg, then the egg cannot be fertilized.
National Library of Medicine
ObGyn Online Library
American Pregnancy Organization
World Health Organisation