Sperm Motility

What It Means, What's Normal, What's Not

Microscopic image of sperm
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The definition of motility is the ability of an organism or fluid to move. Sperm motility refers to the movement and swimming of sperm. Poor sperm motility means that the sperm do not swim properly, which can lead to male infertility. Poor sperm motility is also known as asthenozoospermia.

Why Do Sperm Swim?

Sperm are motile cells. This means that they are cells that make themselves move, which is important when it comes to getting pregnant. For vaginal sexual intercourse to lead to conception, the man generally will ejaculate semen near the cervical canal, at the end of the vaginal canal, though because of motility, any semen ejaculated near the vaginal area can make its way up the vaginal canal and to the cervix.

Semen can also get into the vaginal canal without ejaculation, from what is known as pre-ejaculate. This is a small amount of semen-like fluid that comes out of the urethra when a man is sexually aroused. (This is one reason that the "pull-out method" doesn't reliably work to prevent pregnancy.) 

Sperm are programmed to swim in a way that will help them reach their ultimate destination: the ovulated egg. While the egg is moved along from the ovary into the fallopian tube by tiny hair-like projections called cilia, the egg itself doesn't swim. It more or less floats its way into and through the fallopian tubes with the help of the cilia.

Sperm, on the other hand, move themselves. They must swim up from the cervical canal, into and through the uterus, and, eventually, into the fallopian tube. This is where they meet an ovulated egg. Once there, the sperm must fertilize the egg, which also requires movement.

Research has found that it takes sperm between 2 and 10 minutes after ejaculation to reach the fallopian tubes.

Sperm Motility and Overall Semen Health

Motility is just one measurement of sperm and semen health. Other factors considered during a semen analysis include:

  • Semen volume: How much ejaculate there is, which is measured in milliliters (mL)
  • Total sperm count: How many sperm there are in the semen sample (average is 33 to 46 million sperm)
  • Sperm concentration: How many sperm are in 1 mL of ejaculate
  • Vitality: Percentage of live sperm
  • Sperm morphology: Shape of the sperm
  • Time to liquefaction: The time it takes for semen to naturally change from thick to liquidy (generally 20 to 30 minutes)
  • Semen pH: The acidity of the semen sample (semen that is too acidic can kill sperm)
  • White blood cell count: How many white blood cells are in the semen sample (a very high count can indicate infection)

If motility is the only problem, the odds of spontaneous (unassisted) pregnancy are better than if other issues are present.

Motility Measurements in a Semen Analysis

Motility may be evaluated in a semen analysis in the following ways:

  • Percentage motile: What percentage of all the sperm in a single ejaculate are moving
  • Percentage motile concentration: What percentage of sperm are moving in one measurement of semen, usually presented as millions of cells per mL
  • Total motile sperm count (TMSC): How many sperm are swimming in a single ejaculate (This number has been shown to be most relevant to male fertility prognosis.)
  • Average path velocity (VAP): The speed sperm are moving, measured in microns per second (μm/s)

Progressive Motility, Non-Progressive Motility, and Total Motility

How sperm move is also important. Progressive motility refers to sperm that are swimming in a mostly straight line or in very large circles. Non-progressive motility refers to sperm that move but don't make forward progression or swim in very tight circles. Total motility refers to the percentage of sperm making any sort of movement. This movement can include non-progressive movement.

For example, a sperm that just vibrates in place would be considered motile, but non-progressive. A sperm that zigzags but makes forward progression would be considered progressive. Progressive motility is needed in order for the sperm to swim their way up the female reproductive tract.

How Many Sperm Must Swim Properly

In a man with normal fertility, one ejaculate of semen may contain over 39 million sperm. Not all of those sperm, however, are expected to be completely healthy.

For an ejaculate sample to be considered normal, at least 40% of the sperm should be motile, or moving. This can include non-progressive movement. At least 32% of the sperm should show progressive motility.

A diagnosis of poor sperm motility is usually made based on the percentage of motile sperm. However, research has found that the total motile sperm count is a more relevant measurement.

A total motile sperm count over 20 million is considered to be normal. Lower than 5 million is poor sperm motility. Less than 1 million is severe poor sperm motility.

What Affects Sperm Motility

Usually, when sperm motility is poor, there are other problems found with sperm health. For example, men with poor sperm motility may also have low sperm counts or poor sperm morphology (or sperm shape). Sperm that aren't formed properly can't swim properly.

Sperm motility may be harmed by exposure to chemicals, illness, exposure to heat or cold, lifestyle habits like smoking, or abnormalities of the male reproductive tract, like with a varicocele.

Poor sperm motility may also occur if a man has infrequent sexual activity. In this case, if the first ejaculate collected showed poor motility, a second ejaculate collected soon after should be better.

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