Your Semen Analysis: Sperm Motility

MotilityThey are called swimmers for a reason. Sperm cells are one of nature’s great fascinations. In order to make a baby, they must make an incredible journey traversing toxic obstacles, a labyrinth full of dead ends and sneak past white blood cells that stand guard before reaching the awaiting egg. For life to happen, a sperm cell must be good at swimming. Unfortunately, there are a lot of things that can cause sperm to not swim very well or at all. Because of this, motility is a standard measurement taken during a semen analysis. This article explains how sperm motility is measured, how many motile sperm are necessary for conception, causes of low motility and what men can try to do to improve sperm health.

How Many Swimmers Do You Need to Make a Baby?

Ultimately, just one. But, that’s the smartass answer. In reality, fertilization is like a game of darts with bad eyesight. Sperm have some idea of where to go (due to hormones excreted by the egg) but due to the difficulty of the journey, most end up swimming into nothing. For a better chance of hitting the bullseye, you’d probably want to send in more than one. Andrologists have done a great deal of research to understand the optimal number of motile sperm you’d want to send in. But, remember, it isn’t a strict number you need to get someone pregnant, numbers just represent chances of getting pregnant (hitting the bullseye). In the end, conception can happen against great odds or doesn’t happen even under optimal circumstances. Studies show that sometimes pregnancy can even with low numbers of motile sperm. It also has been shown to NOT happen even when a man has tons of swimmers.

How Motility is Measured During a Semen Analysis

Measuring sperm motility can be a difficult task. Typically, sperm cells are counted and categorized by both speed and direction of movement. To understand the challenge, imagine you were to take a swat at a beehive and record how many bees flew away in a straight line and how many hovered around. Because analyzing sperm motility is difficult, there is a lot of variation from lab to lab and from report to report. You should understand that motility numbers need to be taken with a grain of salt because the numbers are a bit fuzzy, and that’s because the field is full of inconsistent and sometimes subjective methods and standards.

No matter the counting method, the semen sample has to be collected. Collection done right is crucial, and we’ve discussed this elsewhere, but here’s a quick recap. First, is making a high quality sample. Prepare to drink lots of water, and to try your best to get excited (difficult to do if you’re collecting in a doctor’s office). Abstain from ejaculation 2-10 days before producing a semen sample for analysis. While collecting the sample, avoid lotions, lubricants or oils as most are toxic to sperm and can cause results. Make sure you collect all of the ejaculate, especially the first part; that has most of the sperm. Finally, the motility analysis should be done soon. Sperm motility decreases the longer it is outside your body, so be sure the sample is analyzed within 1-2 hours of collection.

Standard Motility Analysis Technique

In the “standard” method, a technician uses a regular microscope slide to count about 100 cells[1]. Of those 100 cells, the technician categorizes them into:

Non-motile: these sperm are not moving. On a semen analysis report, this will sometimes be abbreviated as IM or be called “immotile” or “grade d.”

Non-progressive motile: sperm that are moving but not going anywhere; they are just wiggling, also labeled as NP or “slow” or “grade c.”

Progressive motile: sperm that are moving and actually getting somewhere. Also called PR, or “fast.” Some semen analysis methods call for the technician to divide these progressively motile cells into 2-3 subcategories. You will still sometimes see “grade a/b” or “medium/fast” on such reports. Some believe that judging these subcategories by sight is too subjective, but some extremely well-trained technicians can categorize by sight quite well.

Since the technician counts 100 cells, the number counted for each category represents the percentage of sperm that fall into each category. The technician counts another 100 cells on another slide and makes sure the numbers make sense before reporting to the doctor or patient.

There are some drawbacks to this method, however. One is the obvious human error. A technician counts by looking at the cells under a microscope in a field of view. Sometimes, they can be mistaken. Only well-trained technicians end up being precise[2], [3]. Inexperienced ones can make a lot of mistakes. Because the work is mentally challenging, even well-trained technicians can get tired when straining their eyes to count sperm. Another major source of error is called a statistical sampling error—the idea that the fields of view they’re looking at may not be representative of the whole semen sample. To reduce sampling error, a technician can count more cells, but often if they do, the operator fatigue becomes a bigger factor.

Computer Aided Motility Analysis

To solve operator fatigue, and to remove subjective errors due to judgement calls in determining what is and isn’t progressive, non-progressive, or immotile, andrologists often use cameras and computers to reduce these problems. A camera recording of a microscopic view can help in having multiple eyes look over a sample, and confirm that the numbers are correct. Additionally, operator fatigue and subjectivity can be reduced by simply having a computer do the counting. Such methods are known as Computer-Aided Semen Analysis, or CASA [4].
CASA comes in multiple brands and packages and, depending on what kind your doctor has, is able to measure a bunch of different things about the semen samples. When looking at motile cells, CASA offers a distinct advantage over manual methods[5],[6]. Computers are able to take a recording of a field of sperm, and determine not only which ones are moving, but how fast and in what manner they are moving. The CASA system is then able to take those individual readings and compile them into some summary numbers that gives information about the motile cells being observed. Sometimes, the individual speed measurements for your sperm are measured, and then categorized. You might sometimes see different categories, and numbers associated with the motile categories. Different CASA systems use different thresholds for each category. A common threshold for differentiating sperm speeds is 25 μm/s.[7]

Clearly our benevolent and all-knowing Skynet overlords are infallible. Meh. No. Computers are dumb. CASA has its pitfalls. Andrologists have to make sure that the CASA they’re using is calibrated. Comparing results from different CASA systems can sometimes be difficult[6], [8], [9]. Cameras that record at different speeds sometimes report very different numbers[8] for the same sample. Computer algorithms that calculate VAP (how fast the sperm is swimming) could differ ever so slightly and result in different numbers even for the same sample.[10] There’s no fixed standard for categorizing sperm speed. CASA sometimes mistakenly counts non-sperm debris in your semen as sperm, tending to overestimate the total count (and thus underestimating % motile). The most reliable and consistent number in CASA systems, is concentration of all motile sperm. This number has the highest consistency between systems, camera types, and algorithms. CASA is at least great at finding the moving cells.

Recording Motility Measurement on the Semen Analysis Report

So, motility measurements have their hangups. As a result, the numbers on what you’re supposed to expect are a little inconsistent from study to study. The World Health Organization standards,[1] which is used as the gold standard, requires andrologists to report percent motile cells, rather than cell concentration, so most studies only report percent motile. This leaves the motile concentration and total motile count a mystery in big summary studies.[11]–[14] This is a problem because studies showing the likelihood of getting pregnant show that motile concentration and total motile count, rather than percentage,[7], [15] is the most important factor to look at for motility.

No matter what method being used, your semen analysis report you receive from your doctor will contain similar numbers. However, the manner in which motility numbers are reported can sometimes differ, depending on what philosophies of semen analysis your doctor or andrologist ascribes to. Below are some terms that you might see on a semen analysis report. This list is not expansive, so if you see a term on your own report that you are not familiar with, you should ask the doctor who ordered the test to clarify.

% Motile: This is the most common number you’ll see reported. This is the percent of cells that are motile. You’ll also see this number divided into other classes, such as progressive motile, etc. However, this number does not tell you how many motile sperm you have in total in your semen.

Motile Concentration: The number of cells that are motile in a volume of semen. Usually reported in cells per milliliter (cells/mL) or millions of cells per milliliter (M/mL or × 106cells/mL). You can calculate motile concentration by multiplying the sperm concentration by the % motile.

Total motile sperm count (TMSC): The total amount of motile sperm in your ejaculate. This is calculated if the volume of your total ejaculate is also measured. This is essentially a measure of your “full load” of motile cells you’d be delivering in an ejaculate. Recent studies suggest that this is probably the most important number[7], [15], [16] in your semen analysis report. This number can also be divided into different grades. It is super easy (and much more accurate) for a CASA to divide your sperm cells into “fast” or “slow” using clear speed cut-off values. If this number is not present on your report, you can calculate this number yourself.

VAP: Average path velocity. Sperm wiggle around as they move, but they have a general path they’re moving in. This number is the average speed the sperm is moving at along that general path. This is often report in microns per second, or μm/s.

Calculating your Total Motile Sperm Count

If you have your volume measurement and your motile concentration measurement, it can be calculated by the following:

TMSC = Motile concentration × Semen volume

If you only have % motile, you need use your total sperm concentration to calculate TMSC:

TMSC=(% motile)/100 ×Total sperm concentration × Semen volume

How Many Swimmers Does It Take to Make a Baby?

The amount of motile sperm you make has a strong correlation with being able to get a woman pregnant. It is also not the only important factor. Other factors include total sperm concentration, morphology, etc. Semen analyses need to be taken in as a whole rather than depend on one single number. The consensus on motility seems to focus on TMSC, which is the total load of motile cells delivered in an ejaculate.

One large study of subfertile couples indicates that chances of pregnancy increase substantially when the man’s TMSC is above 5 million cells [15]. Many andrologists classify categories of fertility based entirely on TMSC. The categories are as follows:

Less than 1 million TMSC. This category represents severely low motile counts (also called severe asthenozoospermia). A doctor might recommend to use advanced assisted reproduction methods such as ICSI, which involves injecting sperm directly into an egg.

1 to 5 million TMSC. This category represents moderately low motile counts (sometimes just called asthenozoospermia). A doctor might still recommend assisted reproductive methods like IVF or IUI to achieve pregnancy.

5 to 20 million TMSC. This category means you’re low, but natural pregnancies are still likely within 2 years. A doctor might still recommend IUI to achieve pregnancy.

Above 20 million TMSC. This category means you’re “normal” in terms of motility. If you are still having trouble conceiving, other fertility factors besides motility should be looked at to see if the problem lies elsewhere.

These categories are usually just guides that doctors use to decide if you’d be in need of fertility treatment options, and don’t represent clear cut offs. Studies show that increasing TMSC generally correlates with increasing chances of pregnancies [7], [11], [17].

Is my sperm motility normal?

The best answer comes from the World Health Organization, which reports worldwide measures of semen parameters. The WHO reports motility only in percentage, so it is difficult to say what the typical total motile count is. In general, 50% of men worldwide have a total motile percentage above 61%. Only 5% have less than 40% motility measurement, so if you’re below that, this might cause concern.

Motility tends to decrease with age, with it peaking sometime before age 25 and gradually lowering over time [18]. Additionally, some men experience seasonal variations in their motility measurements [19], due to the importance of temperature on sperm production.

What Could Go Wrong?

Low motility numbers is referred to as asthenospermia. Asthenozoospermia can range from zero motile sperm to low numbers. The WHO defines asthenozoospermia as falling below 40% motility, but some prefer 20 million total motile count as a measure instead [1], [15].

In the general population, many men in Western countries suffer from suboptimal semen quality, as much as nearly 80% have some aspect of their semen analysis below optimal numbers [20]. It is not clear what percentage of that were due to low motility. However, by looking at subfertile or men diagnosed as infertile, we can see how low motility can impact fertility. 81.4% of one large population of men diagnosed with infertility have astenozoospermia [21].

Furthermore, your motility numbers and other semen parameters can all be normal but you might still have a problem with motility. The limitations of laboratory measurements means that there’s lots of factors missing when a technician analyzes your semen. Perhaps your sperm can’t survive the environment of your partner’s body, or your sperm have something wrong with their hyperactivation mechanism, the process where a sperm senses an egg nearby and goes into turbo-motility mode [22].

What Causes Low Motility?

The causes are many, and we can only briefly describe them here. Watch for follow-up articles that go more in-depth.

Genetic factors can produce low or non-existent motility. Some genes that directly make the sperm move (such as proteins in the tail) can be mutated [23], the production factory in your testicles could be mutated, or some metabolic diseases can cause impaired sperm production by causing your body’s hormones or nutrition to be out of whack, also causing you to make immotile sperm in the testicles [24].

Next, there’s metabolic and environmental factors. What you eat or what condition your body is in may affect motility. Sickness [24], poor nutrition [25], smoking [26], heat exposure, and toxin exposure [27] all could impact motile sperm count.

What can be done about low motility?

If you’ve found you have genetic-based reason for low motility, treatment might be possible for some hormonal disorders, but often you’d need to resort to assisted reproduction techniques if you have a genetic reason for low or no motility.

Environmental factors can be changed, and that sometimes has an impact on count and motile count. Avoiding cigarettes, alchohol, heat, and eating healthier can sometimes improve motile count. Some supplements can also boost motile counts. Antioxidant vitamins, such as Vitamin A, E, or C can have a positive impact on motility [28]. Vitamin D promotes the factors that directly cause sperm tails to wiggle, and intake of that vitamin can also have benefits for your motility [29].

Keep in mind, that when you are getting checked up on your semen parameters, that motility count is super important, but it is not the sole deciding factor in your ability to get pregnant. Read up on all these other factors, such as morphology, total count, and semen quality elsewhere.


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Scientist passionate about sperm, chemistry, microbiology & baking bread.

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