Sperm Density, Motility, and Total Motile Count
Sperm density is the number of sperm that are present per milliliter (cc) of semen. Sperm density is typically reported in units of millions of sperm per cc.
While the latest WHO criteria designate a normal sperm density as 15 × 106/cc or more, I think a sperm density of 40 × 106/cc or more may be more appropriate for a truly normal sperm density. However, using the total motile count (TMC) is arguably an even better way of judging male fertility potential.
A few commonly used terms regarding sperm density:
Oligospermia: any sperm density less than what is considered normal
Severe oligospermia: typically considered to be less than 5 million sperm/cc
Azoospermia: no sperm at all seen in the ejaculate
Virtual azoospermia: only a very small number of sperm (sometimes defined as less than
Of note, azoospermia and virtual azoospermia are explored in greater detail in separate sections of this website.
Motility, or the number of sperm that are actually swimming, is important for success with natural intercourse and intrauterine insemination, because the sperm need to be able to swim up the fallopian tubes, where fertilization takes place. For IVF, sperm motility is not quite so important since sperm can be injected directly into an egg in the lab with the use of intracytoplasmic sperm injection, or ICSI. However, the sperm that are injected need to be alive, and motility is an accurate marker of this (i.e. if sperm are moving then they are live, although sperm that are not swimming may be alive as well). Decreased sperm motility is sometimes called “asthenospermia”.
important aspects of sperm motility:
Total motility: the total percentage of sperm that are actively swimming (the latest WHO criteria define normal total motility as 40 percent or more)
Motility grade: how well (on average) the sperm are swimming. Although there is some variability between labs, degrees of motility are generally defined as:
0 No motility
1 Sluggish movement with absent or minimal forward progression
2 Poor to fair activity with forward progression
3 Good activity with forward progression, tail movement visualized
4 Full activity with tail movement difficult to visualize and movement rapid across the field
Normal motility is typically described as a grade of 2 or more. Sperm with an activity grade of 0 or 1 are less likely to be able to effectively swim up the fallopian tubes where egg fertilization occurs. It is important to remember, though, that the reported motility grade indicates the "average" of how well the sperm are swimming. So if a man has a motility grade of 1, there are still most likely a certain percentage of sperm present with better forward progression and which are capable of traveling up the fallopian tubes (unlike the majority of their fellow sperm in that particular sample).
Whereas most fertility labs report sperm density in the same way, labs tend to employ a much wider range of methods to report sperm motility. The most common way is to report the total percentage of sperm that are swimming as well as their average grade of motility. Most labs also report the percentage of cells that swim with “progressive motility” (generally considered grade 2 or higher). The latest WHO guidelines say that normal “progressive motility” is 32 percent or more.
Some labs go further and break down what percentage of sperm fall into each motility grade, for example:
25% Progressive motility (Grade 3)
15% Slowly progressive (Grade 2)
10% Twitching (Grade 1)
50% Non-motile (Grade 0)
Certain labs would report this as total motility of 50 percent (those in grades 1, 2, or 3), while others might specify 40 percent progressive motility (those in grades 2 and 3 only).
Example: A man with ejaculate volume of 1.0cc, sperm count of 10 million sperm/cc, total motility of 50%, and progressive motility of 25%. So he would have a total of 10 million sperm in his ejaculate and 5 million would have some degree of motility. 25% of the motile sperm would have a motility grade of 2 or higher, which would translate into 1.25 million sperm swimming with at least a motility grade of 2.
One issue to consider regarding motility is the presence of anti-sperm antibodies (ASAs), which can cause sperm to stick together, thereby decreasing their motility. Most good fertility-specific labs will note on the semen analysis report if significant clumping (also called agglutination) of sperm is seen. Sperm clumping combined with poor motility is suggestive of the presence of ASAs; their presence can be confirmed on repeat semen analysis with direct (immunobead) ASA testing.
More detailed information on anti-sperm antibodies can be found in the above separate section on this website.
The Problem with Using the Standard Semen Parameters
Most physicians rely on sperm density and motility to determine the fertility potential of men. The problem with this approach is that when viewed in isolation, these parameters can provide an inaccurate picture of the actual number of swimming sperm. The reason is that the testicles provide only about 5 percent of the volume of ejaculate that is released during ejaculation. The other 95 percent of the fluid comes from the seminal vesicles and prostate gland, and their fluid production can vary from day to day and has nothing to do with testicular sperm production. In essence, the prostate and seminal vesicles provide the fluid “vehicle” for delivery of the sperm, while the testicles provide the sperm “content.” What determines the actual fertility potential of the semen is the total number of swimming sperm that are present in the entire ejaculate, not the amount of sperm present per unit of semen.
An analogy would be to try to judge how much blue dye is in two different amounts of water. Let’s say you added one cup of concentrated blue dye (representing the sperm) into a gallon of water (lower ejaculate volume) and another one cup into a whole bathtub of water (high ejaculate volume). The amount of dye present is the same in both amounts of water, but the density of dye in the bathtub is going to be significantly lower than in the gallon of water.
The same concept applies to semen. The testicles are adding a certain amount of sperm into the ejaculate, and this amount of sperm is what you are trying to measure. Meanwhile, the ejaculate volume is going to vary depending on the production of fluid by the seminal vesicles and prostate. We want to know the total number of swimming sperm present in the entire ejaculate and not just how concentrated or diluted the sperm is within the ejaculate fluid. The way to determine this total number of swimming sperm is to calculate the total motile count (TMC).
Total Motile Count (TMC)
The total motile count (TMC) gets around the problem of fluctuating ejaculate volumes by combining the sperm density, motility, and ejaculate volumes together to provide the total number of swimming sperm that are present in the entire ejaculate.
Some labs report this number under the label “TMC,” while others call it something slightly different, such as “total motile sperm,” “motile sperm count,” or some other similar variation. The key to identifying what the lab is talking about is the unit of measure, which should say “__ million” (or “__ × 106”) for TMC, as opposed to “__ million per cc” (or “__ × 106/cc”) for sperm density. The other differentiation that you need to keep in mind is the “total count,” which is the total number of both swimming and non-motile sperm (and is not as useful a number).
If the TMC is not reported, it can be easily calculated by using the following equation:
(Sperm Density × Ejaculate Volume × Total Motility) ÷ 100
For example, an analysis with an ejaculate volume of 2.0 cc with a sperm density of 30 × 106/cc and a total motility of 50 percent would have a TMC of (2.0 × 30 × 50) ÷ 100 = 30 million sperm.
What Is a Normal TMC?
In terms of successfully establishing a pregnancy with natural intercourse or IUI, higher numbers of total swimming sperm are better. A TMC of 20 million sperm is getting into the territory of good fertility potential, while I believe that a completely normal TMC is typically considered to be 75 million sperm or more (though some experts in male infertility use different ranges). A minimum TMC of 5 million sperm is typically considered the lower cutoff for being a candidate for intrauterine insemination (IUI).
Why Calculating TMC Is Important
Consider a man who has a sperm density of 30 × 106/cc with an ejaculate volume of 1.1 cc and a total motility of 50 percent. His calculated TMC is 16.5 × 106.
Now, let’s take a second man who has a sperm count of only 6.6 × 106/cc and the same motility, 50 percent, but an ejaculate volume of 5.0 cc. His calculated TMC is the same: 16.5 × 106.
Both of these men have the same number of swimming sperm in their ejaculate. But if the standard WHO definitions are used, the first man would be considered well within the normal range (and would probably not get a recommendation to have a male fertility evaluation, even though he should), and the second man would be considered to have significantly abnormal semen parameters.
Motility Grade and TMC
One very important consideration to keep in mind when evaluating TMC is the average motility grade. If most of the sperm are only twitching, then their fertility potential is not going to be very good for natural intercourse or IUI. Therefore, a TMC is considered “normal” only if the average motility grade is 2 or higher.
How do you calculate TMC if the lab has broken down the percentages of sperm with each different motility grade? Do you include the grade 1 (twitching) sperm in the calculation of total moving sperm? There is no absolutely correct answer to this. I tend to include grades 1 through 3 in the TMC calculation, as this was how it was done in studies that established the “normal” sperm density cutoffs of 40 to 55 million sperm.
[Note: Some labs calculate a “Total Progressive Motility” on their semen analysis reports. Instead of using the total motility for calculations, they instead use the progressive motility percentage. I prefer to use the total motility to calculate TMC, as these are what the calculations used from the Bonde and Slama studies discussed below.]
Where Does the “Normal” TMC Definition Come From?
How did a TMC of 75 million sperm or higher come to be considered “normal”? That figure is based on two studies that looked at natural pregnancy rates and sperm density.
The first looked at 430 couples and their chances of establishing a pregnancy within six months of starting natural intercourse. The study, conducted by J. P. Bonde and colleagues and published in the Lancet in October 1998, found that chances of pregnancy increased as the man’s sperm density approached 40 × 106/cc, but that above 40 × 106/cc the odds did not improve further.
The second study, carried out by R. Slama and colleagues and published in Human Reproduction in February 2002, looked at 940 couples who achieved pregnancy naturally and found a correlation between decreasing time to achieve pregnancy and rising sperm counts up to 55 × 106/cc; after that level, pregnancy did not occur more quickly.
The conclusion we can reach from these studies is that sperm densities of 40 to 55 × 106/cc may improve the chances of natural pregnancy. I tend to be a little conservative and use as a goal the lower sperm density cited in the first study mentioned above (40 × 106/cc). In this study, the average semen volume was 3.14 cc and the average motility was 61.4 percent. Plugging these figures into the equation for calculating TMC produces (3.14 × 40 × 61.4) ÷ 100 = 77 × 106 sperm. The studies showed an increasing chance of natural conception up to this level, but no significant further improvement with higher TMC numbers.
You should be aware that this interpretation of a “normal” TMC may be controversial, and other male fertility experts may have other definitions of a normal range. However, I feel that the available studies suggest that a goal of at least 75 million swimming sperm is reasonable.