What is Sperm Motility?
Sperm motility refers to the sperm cell’s ability to move, which is achieved through a swimming motion made by its tail.
Having sperm that are unable to swim properly can lead to infertility in men. The medical term for poor sperm motility is Asthenozoospermia (also called asthenospermia).
Why Sperm Need to Swim
Sperm cells are motile in nature, meaning that they are able to move themselves. This ability is vital when it comes to successfully penetrating and fertilizing the egg.
In order for conception to occur from sexual intercourse, the man ejaculates semen near the cervical opening (at the end of the vaginal canal). Due to its motility, the sperm is able to travel up the vaginal canal and into the cervix after semen is ejaculated inside the vagina
Semen is also sometimes able to make it into the vagina without ejaculation, from what is termed as “pre-ejaculate”, or “pre-come”. Pre-ejaculate is a small amount of seminal fluid that may come out of a man’s penis when he is sexually aroused (which is one reason that “pulling out”, or coitus interruptus, is not a reliable method of birth control).
Sperm are able to swim in such a way that will help them achieve their ultimate goal: reaching and penetrating the ovulated egg. Although the egg is unable to swim like sperm cells can, it gets transported from the ovary into the fallopian tube by tiny hair-like extensions called cilia.
With the help of these cilia, the egg is pretty much able to glide its way into and through the fallopian tubes.
Sperm, however, are able to move themselves. They must swim up into the cervical opening, then into and through the uterus, and finally make it to the fallopian tube where they reach the ovulated egg.
At this point the sperm must fertilize the egg, where even more movement is required. Research shows that sperm can reach the fallopian tubes in anywhere from 2-10 minutes after ejaculation.
Sperm Motility and Overall Semen Health
Sperm motility is only one aspect of sperm and semen health. When taking a semen analysis, 0ther factors are also considered, including:
- Morphology: The shape of the sperm.
- Total sperm count: The number of sperm found in the entire semen sample (the average is 33-46 million).
- Concentration: The number of sperm found in 1 mL of semen.
- Sperm vitality: The percentage of sperm cells that are alive.
- Semen volume: The amount of the ejaculate sample, measured in milliliters (mL).
- Semen pH: Measures the alkalinity or acidity of the semen sample (overly acidic semen can kill sperm).
- Time to liquefaction: The amount of time for the semen takes to turn to a watery consistency, or liquify (typically 20-30 minutes).
- White blood cell count: The number of white blood cells found in the semen sample (a large amount could indicate an infection).
If the only issue with the semen analysis is motility, the chances of a natural pregnancy are better than if other issues are found.
Motility Measurements in a Semen Analysis
Motility may be evaluated in a semen analysis in the following ways:
- Total Motile Sperm Count (TMSC): Refers to how many sperm are swimming in a semen sample. This number is considered to be most important indicator when assessing male fertility.
- Percentage Motile: The total percentage of all moving sperm found in a single sample of ejaculate.
- Percentage Motile Concentration: The percentage of moving sperm found in a single semen measurement, typically indicated as millions of cells per mL.
- Average Path Velocity (VAP): The speed at which the sperm move, measured in microns per second (μm/s).
- Progressive Motility: Measures the percentage of sperm that are mostly swimming in a straight line, or in wide large circles. Progressive motility is necessary for the sperm to make their way through the female reproductive tract.
- Non-Progressive Motility: The percentage of sperm that are moving, but either aren’t making forward progression or are swimming in small circles. A sperm making forward progression even though swimming in a zig-zag motion would still be considered progressive.
- Total Motility: The total overall percentage of sperm that display any type of movement, including non-progressive movement. For instance, a sperm that vibrates in place would qualify as motile, but with non-progressive motility.
How Motility is Graded
A detailed semen analysis will categorize sperm motility into one of the following grades:
- Grade A – Sperm cells that demonstrate progressive motility and swim quickly in a straightforward direction.
- Grade B – Sperm cells that demonstrate progressive motility but move forward slowly and/or in a non-forward motion.
- Grade C – Sperms with non-progressive motility that are able to move their tails, but unable to move forward.
- Grade D – These sperms are non-motile and show no movement at all.
Sperm cells with motility grades of C and D are considered to be poor, indicating low-quality sperm are being produced by the testicles and that they are not functioning normally. In this type of situation, successfully achieving a natural pregnancy can be difficult.
Normal Sperm Motility
A man who has normal fertility will produce a semen sample containing around 40 million sperm. However, not all of the sperm in the sample are expected to be completely healthy.
For a sample of ejaculate to qualify as normal, at least 40% of the sperm should be motile, or moving. This also includes non-progressive movement.
Progressive motility should be found in at least 32% of the sperm.
Diagnosing poor sperm motility is normally based upon the percentage of motile sperm. That said, studies show that the total motile sperm count provides a more meaningful measure.
A total motile sperm count that is considered to be normal if the sample contains over 20 million motile sperm cells. Fewer than 5 million is considered to be poor sperm motility, and less than 1 million is considered to be extremely poor sperm motility.
What Affects Motility
Normally, there are other issues found associated with sperm health when poor sperm motility is seen. Men having poor sperm motility may also have poor sperm morphology or low sperm counts, for example.
Sperm motility can be negatively impacted by lifestyle habits (like smoking and drinking), illness, exposure to chemicals, exposure to heat or cold, genetics, or conditions involving the male reproductive tract.
A man who does not frequently engage in sexual activity may also demonstrate poor sperm motility. However, if the initial semen sample indicates poor motility, a follow-up sample soon after should show better results.