About one in four couples that undergo an infertility evaluation will find out that infertility is due to a "male factor" of some sort. This “male factor” could be many different things, but in most of these cases, the issue has something to do with the man's sperm. Consequently, a standard semen analysis includes measures of semen volume, sperm concentration, sperm motility, and sperm shape among other things. Yet even before semen analysis takes place in the lab, many men with fertility issues wonder whether their semen is “normal” or not. While your fertility specialist can explain many of these issues, this article covers the basics.

The Difference Between Sperm and Semen

The terms sperm and semen are often used interchangeably, but they are not quite the same thing. The term sperm is the same as spermatozoa, which are the individual cells that carry DNA. Sperm/spermatozoa are the cells with tails that propel them forward—what most people think of when they visualize a sperm cell. Semen, on the other hand, is the thick fluid that is expressed during ejaculation. Under normal circumstances, semen contains tens of millions of sperm. But semen also contains many other substances. In addition to sperm, semen contains secretions from the testicles, prostate, and Cowper’s (bulbourethral) glands. These secretions contain various proteins, sugars (e.g. fructose), electrolytes, water, and cells (e.g. white blood cells), which gives semen it is thick consistency.

Why is the difference between sperm and semen important?

While you can plainly see semen without a microscope, it is impossible to see sperm without a microscope. Semen may contain sperm, or it may not. Semen may contain high, normal, or low concentrations, or no sperm cells at all. While someone may have a relatively small or large volume of semen, without testing it is impossible to know the concentration of healthy sperm within that semen. The number of healthy sperm contained within the semen is most important for fertility because those sperm cells are what combine with egg cells to create new life.

What is a normal volume of semen?

After studying semen samples from thousands of healthy men, the World Health Organization developed and published guidelines on what is normal semen, including semen volume. The average semen volume is 3.7 mL, or one-eighth of an ounce. The WHO determined that the lower level of normal is about 1.5 mL. Conversely, a small portion of men will have very large volumes of semen, defined as 6.3 mL or greater.

For the most part, the number of sperm contained within semen is proportional to the volume of semen. In other words, as the volume of semen increases, so does the number of sperm for most healthy men. Yet this is not necessarily the case, as we will see.

What is the concentration of sperm in semen?

In order for men to be fertile, they need to express a minimum number of sperm in the ejaculate. This makes sense when you consider that most sperm veer off course or die before reaching an egg. So it becomes a numbers game; the more sperm, the greater the chances of one meeting and joining with an egg. If we again consider the WHO’s study of fertile men, they report the lowest sperm concentration that still considered normal is 1.5 million sperm cells per milliliter. Once the concentration drops below this value, it could interfere with fertility. That said, men who are considering in vitro fertilization (IVF) may successfully fertilize and egg with sperm concentrations as low as 10 million sperm cells per milliliter, and maybe less.

What is hypospermia?

Here is where things get a little confusing. A medical term preceded by hypo- means “lower than” or “beneath.” Hypoglycemia means abnormally low blood sugar, for example. Hypospermia does not mean abnormally low sperm, it means abnormally low semen volume. An abnormally low sperm count would be referred to as oligospermia. If the semen contained no sperm, it is referred to as azoospermia. If a man consistently produces less than 1.5 mL of semen per ejaculation, he is said to have hypospermia.

What causes hypospermia?

There are many causes of low semen volume. Some are easily corrected and others are not. For example, men who ejaculate frequently reduce the amount of semen available for release. Therefore, when they ejaculate the volume is relatively low. The solution for this cause of hypospermia is to simply abstain from ejaculation for 2 to 7 days. The secretions and sperm replenish during that time, and semen volume is once again normal.

Other causes of hypospermia are considered "pathologic," and may require specific medical attention by a urologist or fertility specialist.

Pathologic causes of causes of hypospermia include:

In general, hypospermia or low semen volume only interferes with fertility if there are also not enough healthy sperm contained within the semen. Your doctor can diagnosis and potentially treat hypospermia.

What causes hyperspermia?

Hyperspermia is a condition in which the semen volume is abnormally large. In most cases, hyperspermia does not interfere with fertility. In fact, if the semen contains an adequate concentration of healthy sperm, higher volumes actually enhance fertility. However, men with very high semen volumes can suffer from infertility. This is because the concentration of sperm in the semen is too low. The semen contains more of the substances that are not sperm cells (i.e. secretions), which means the semen is too dilute to fertilize an egg.

Unfortunately, there is no specific medical treatment for hyperspermia. However, fertility specialists may be able to overcome the condition for in-office procedures, such as in vitro fertilization. For example, hyperspermia may be treated by the “split ejaculate” technique during sample collection or similar process.

Summary

Semen is the vehicle that carries sperm, which are the cells that carry DNA and unite with an egg for fertilization. Semen contains sperm cells, proteins, electrolytes, sugars, water, and other cells. Semen is produced by the testicles, seminal vesicles, prostate, and bulbourethral glands. The chance of a successful conception increases as the number of healthy sperm cells in the semen increases. Hypospermia is a condition where the volume of semen in the ejaculate is less than 1.5 mL. There are many causes of hypospermia, and some can be treated. Hyperspermia is a condition where semen volume that is abnormally high. Hyperspermia usually only interferes with fertility if the ejaculated semen has an abnormally low concentration of sperm cells.