What is normal semen?

Semen is usually white or grey, but can occasionally appear yellowish. Pink or red semen suggests that blood is present. Although this is only rarely due to a serious health problem, men with semen that seems bloodstained should seek advice from their family doctor.

Semen clots almost immediately after ejaculation, forming a sticky, jelly-like liquid. It will liquefy again in 5 to 40 minutes. It is quite normal for semen to form jelly-like globules and this does not indicate any health or fertility problem. Failure of clotting and subsequent liquefaction can cause fertility problems.

The average volume of semen produced at ejaculation is 2 to 5ml. Volumes consistently less than 1.5ml (hypospermia) or more than 5.5ml (hyperspermia) are probably abnormal. Lower volumes may occur after very frequent ejaculation and higher volumes are seen after prolonged abstinence.

The World Health Organization provides a definition of a 'normal' sperm count:

* the concentration of spermatozoa should be at least 20 million per ml.

* the total volume of semen should be at least 2ml.

* the total number of spermatozoa in the ejaculate should be at least 40 million.

* at least 75 per cent of the spermatozoa should be alive (it is normal for up to 25 per cent to be dead).

* at least 30 per cent of the spermatozoa should be of normal shape and form.

* at least 25 per cent of the spermatozoa should be swimming with rapid forward movement.

* at least 50 per cent of the spermatozoa should be swimming forward, even if only sluggishly.

It is quite surprising how many dead and abnormal sperm can be present in a 'normal' sample.

Measuring sperm count is a very technical business and results can be affected by many factors, including the length of time between ejaculation and semen sample analysis, and how the sample is kept when being transported to the lab.

There can be enormous variation in sperm count in an individual, even over a few days. It is important that at least two, preferably three or more, samples are analyzed, each at least two to three weeks apart. A single sample is inadequate to assess semen quality.

Sperm count is only an indication of fertilizing capacity and a normal count does not guarantee success. In addition, more is not necessarily better, as too high a sperm count can also result in fertility problems.