Sperm must travel within the female reproductive tract to reach the site of fertilization. Sperm motility is measured in two ways: percentage of sperm exhibiting any kind of movement, and the quality of this movement, which is called the forward progression. "Low sperm motility" usually refers to the percentage of sperm that are moving, while the progression is described separately. Both types of abnormalities may be caused by varicocele, partial ejaculatory duct obstruction, or genetic factors. They are rarely affected by hormonal problems. A decrease in forward progression may sometimes be explained by the viscosity, or thickness, of the seminal fluid. This is overcome by a simple lab treatment while processing a semen specimen for insemination.
Normal Sperm Motility is 40 % or more of the sperm are motile and mean sperm velocity is 20 (µm/s (micro meter / second)) or more.
Asthenospermia is defined as less than 40 % motility, frequently with subnormal sperm velocity.
Oligoastheno spermia (OAS) is a condition in which low sperm count associated with low sperm motility.
Low sperm motility can greatly affect getting pregnant. While it is not as common of a problem as having a low sperm count, low sperm motility can be much more difficult of a fertility problem for a man to address than a low sperm count. While low sperm count can often be treated with a simple lifestyle change or with a medication of one sort or another, problems with low sperm motility and the way it affects getting pregnant more often will require a more aggressive, complicated, and costly solution.