There are several important tests of a man’s sperm and semen that should be carried out to assess a man’s fertility. These include:

During an orgasm most men ejaculate around two to five millilitres (up to a teaspoonful) of seminal fluid. If the volume is less than this, the man may not be producing enough secretions.

There are normally more than 40 million in each millilitre of seminal fluid. One of the miracles of fertility is than an average man produces around 200 million sperm in each ejaculate in only a teaspoon of fluid. Though it only requires one sperm to fertilise an egg, it seems almost unbelievable that there still may be a problem if there are fewer than 20 million in each millilitre.

A count much lower than 20 million per millilitre does not necessarily mean that a man is sterile. A few men are fully fertile even when they produce only 2 or 3 million sperm per millilitre of semen.

At least 40% of the sperm should be moving. The quality of movement is important; there are now sophisticated machines in many laboratories that can measure the speed of an individual sperm’s movement under the microscope and detect, most importantly, whether it is swimming in a straight line.

The shape and structure of a sperm (that is, what is referred to as its morphology) are also important. All men produce some abnormally looking sperm, but a healthy sample normally contains around at least 65% normal looking sperm.

Some men produce very ‘thick’ seminal fluid. Although seminal fluid when first produced may be rather jelly-like, or contain little lumps of jelly, it should liquefy within a reasonably short time after ejaculation.

Most laboratories will record whether many or any sperm are stuck together. ‘Clumping’ may indicate infection or possible antibodies to the sperm. The presence of many bacteria or great numbers of white cells is also indicative of some infection that may impair the sperm function, particularly motility.

If there are no sperm in the semen after ejaculation, this may be because there is a blockage either above or below the seminal vesicles. The seminal vesicles produce fructose, a form of sugar that can be easily measured in the semen. If the semen is low in fructose, this suggests that the blockage is below the seminal vesicles.

Some laboratories do specific tests for antibodies attacking the sperm. Antibodies are produced by our immune system usually as a response to injury or infection. These are usually produced as vital part of the body’s defence system. However, when they attack the sperm they can prevent them from moving or working normally.

I must emphasise that a single normal sperm count is not by itself an indication of a man being fully fertile. On the other hand, one abnormal or low count does not necessarily mean that there is anything wrong. Most men occasionally produce poor quality semen, especially if they have had a recent illness or have been under stress. Good clinics will, therefore, assess a man’s fertility on the basis of several sperm counts and usually do specialised sperm function tests as well.

Some infertile men produce sperm with DNA damage and this can be seen under the microscope using special staining techniques. There are various tests to measure this, including the number of ‘fragmented’ sperm and various molecular chemical tests which an andrology clinic may wish to undertake. There is only a poor correlation between DNA damage and failure of fertilisation but it is widely reported that sperm DNA damage is associated with a poorer success rate during IVF.

The post-coital test is an examination that has largely been discarded in many clinics, but it has its uses. At a routine internal examination, approximately six to 36 hours after sex, a sample of mucus from the cervix is gently sucked into a small pipette. The presence of still-moving sperm gives limited information about the ability of the sperm to survive for a longer period of time inside the entrance to the uterus.

This test needs to be done in the first half of the menstrual cycle, just before ovulation when the mucus is less viscous and easily penetrated by sperm. It may help the specialist to assess not only the man’s fertility but also whether the woman is ovulating normally and has a healthy cervix.

There are so many reasons why a post-coital test may be negative that this test is less relevant than it used to be. For one thing, women who have not ovulated tend to have rather thick, impenetrable mucus. Although many clinics and specialists have abandoned it there is recent evidence from researchers in Holland that a positive test is strongly correlated with a greater chance of spontaneous pregnancy in up to 75% of couples.

Despite countless breakthroughs in medical science, we still do not understand why some pregnancies will end in tragedy. For most of us, having a child of our own is the most fulfilling experience of our lives. All of us can imagine the desperation and sadness of parents who lose a baby, and the life-shattering impact that a disabled or seriously ill child has on a family.

Professor Robert Winston’s Genesis Research Trust raises money for the largest UK-based collection of scientists and clinicians who are researching the causes and cures for conditions that affect the health of women and babies.

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