Sperm is under attack. From environmental oestrogens, to the wrong underpants, to the excesses of modern living, horror stories about the threat to sperm are all over the news. But what do we really know about sperm? Allan Pacey gives the layman's guide to semen analysis, sperm counts and whether boxer shorts really are the underwear of choice.

When a couple first go to their doctor complaining of infertility, there are a number of tests that can be arranged to rule out obvious problems in either partner. A blood test will quickly confirm whether or not the woman is ovulating and a type of X-ray procedure can check that her Fallopian tubes are not blocked. For the man, one of the first steps is to ask him to produce a semen sample for analysis to check the quality of his ejaculate. Armed with this information, the doctor can make an informed decision as to the where any problem might lie and if appropriate suggest a course of treatment. Sounds easy doesn't it?

A semen analysis is, however, a complex business. It involves the measurement of 12 or 13 different within about an hour of the sample being produced. This is why many units require that samples for analysis be produced on site, since a specimen that has been sitting around for an hour or two (or has been sent to the laboratory by post!) will have degenerated too much for any test result to be meaningful.

Unfortunately, however, not all couples are lucky enough to live near to a specialist fertility unit. Within the United Kingdom, a general laboratory in the local hospital performs the majority of semen analyses. Here, samples are not produced on site but at home, and patients are charged with the responsibility of getting the semen to the laboratory within an hour of its production. This lack of specialist resources is rooted in the history of male fertility evaluation and the fact that, until recently, it has been of relatively low priority.

Whilst woman's reproductive issues have been looked after by the gynecological profession, men have no such speciality to which they could turn to help. Until recently, if a man had a low sperm count, it was considered unfortunate but nothing could be done to correct it. Only ten years ago, donor insemination was still the major therapy, for a man with severe oligozoospermia (low sperm count). And although IVF could be useful in some circumstances, it still required several million sperm to be recovered from a man's ejaculate. In this climate, there is little wonder that art of semen analysis was not given a high priority, even by the laboratory staff who were asked to perform it.

In 1993, the British Andrology Society (BAS) funded a small study designed to evaluate the semen analysis results generated by 20 laboratories that had volunteered to take part. The results indicated an alarming picture - enormous discrepancies in the results from different labs. At the time the BAS study was groundbreaking, but similar studies have now taken place in several other European countries, as well as in the United States and Australia. All paint the same picture and suggest that despite the best efforts of the WHO to standardise methodology, there is a lot of work still to do. As such, one wonders how many patients have been denied access to infertility treatment because of the mistaken belief that the male partner is normal when he is not. Or how many couples have been offered the wrong treatment, or either partner had been subjected to further and more expensive or uncomfortable (surgical) investigations in order to reach a diagnosis. Such a situation would not be tolerated in other aspects of medicine where patents' lives are at risk, but when fertility is the issue this seems to be an acceptable situation.

The BAS study also triggered an historical study of data on sperm count. The best known of which was published in the British Medical Journal in 1990 by a Danish group led by Neils SkakkebÊk. At the time it received worldwide media coverage and it is still quoted as the definitive study that has proved that sperm counts had fallen over the preceding 50 years. The SkakkebÊk has been widely criticised, but for all its faults it marked a turning point in our perception of male infertility. Unlike other reports before it, this one opened the eyes of scientists, doctors, politicians and the public to the possibility that male fertility may be under assault and required immediate and further study before it was too late.

Following the publication of the SkakkebÊk report scientists and environmentalists began searching for possible environmental factors that might be affecting male fertility and influencing semen quality. This search began, even though the hypothesis that a decline in sperm counts had occurred had not ñ and has still not - been proven. But, the underlying concern was that if there is something about our modern environment that is potentially affecting semen quality, then there is perhaps some urgency to understand what it is. Several theories have now been proposed but the most popular is that chemicals in the environment with oestrogen mimicking qualities are the most likely agents to affect semen production. Perhaps surprisingly, the direct evidence to support this hypothesis is largely circumstantial but until someone can prove otherwise it would seem the most likely candidate.

From what we currently know about the testes, there are a number of stages at which spermatogenesis (sperm production) might be influenced. The first is genetic. We are rapidly learning about a number of genes that if deleted or mutated can lead to poor sperm production. Hopefully, the human genome project will assist in the better understanding of the genetics of testicular function, but at the present time our knowledge is incomplete. The second stage occurs before a man is even born by interfering with testicular development and differentiation in utero. This is thought to occur because the number of sperm nourishing (Sertoli) cells in his testes largely determines a man's sperm output as an adult, and it is suspected that the number of Sertoli cells is fixed at or soon after birth. As such, any factors that a man's mother comes into contact with during her pregnancy might have the potential to influence the sperm count of her future son. This is how environmental oestrogens are thought to have their effects.

A man's mother can also influence the fertility of her son in other ways, and there is some evidence to suggest that a man's sperm quality (in terms of motility) is negatively associated with the age of his mother at the time of his conception. The sperm from offspring of older mothers swim less well than the sperm from sons of younger mothers. This would seem to be related to an increased mitochondrial mutation rate as we get older and since we inherit our mitochondria from our mothers and the sperm rely on them to generate energy for movement, then this relationship is perhaps not surprising. From these examples, it is clear that there are many influences on male fertility that are completely outside a man's control. So what about factors that are under a man's control ñ such as his diet, his lifestyle and his occupation? Are there things that should be avoided if he is to stand any chance of improving his sperm quality?

A question often asked is whether smoking or drinking are bad for sperm quality. There is now convincing data to suggest that heavy smokers and drinkers are likely to have poorer sperm quality. Similarly, some dietary studies have suggested that men should eat a balanced diet, with the recommended daily intake of vitamins and minerals to optimise his sperm production. Type of underwear is a common point for discussion, but there is no evidence to suggest that there is any difference in fertility between men who wear boxer shorts versus those that wear Y-fronts. That hasn't stopped some manufacturers developing undergarments (advertised on the Internet) with apparently beneficial spermatogenic qualities.

Occupational factors are perhaps the most important to consider, but although we know about the negative effects of a handful of chemicals, we are largely ignorant about most of the compounds that men come into contact with in the workplace. The assault on the testes does not have to be chemical in nature, however. Recent reports suggested that men who spend a long time driving might have lower semen quality, possibly as a result of their testicles becoming too warm. Once again this is controversial and before men desert their cars in favour of their bicycles, a similar report published last year suggested that too long in the saddle could also be bad for sperm production.

For the most part, we still do not know why the sperm quality of some men is so poor and moreover there are no known therapies that have been shown to increase the quality of a man's semen. Sadly, this does not stop some men being given bad advice or grasping at little more than old wives tales as a potential solution. It must be out of desperation that some men choose (or are upbraided by their wives) to immerse their testicles in cold water for several minutes each day in an attempt to improve their sperm quality. However, admirable or masochistic this may be, it is perhaps a sad reflection of our knowledge base of male infertility that men resort to this kind of measure to try and improve their semen quality. We need more research with carefully designed studies and appropriately performed semen analysis to study male fertility in finer detail. Only then will we be able to identify those factors that should be avoided at all costs and stand a good chance of developing more simple therapies for men and their sperm.

Allan Pacey is lecturer in Andrology at the
University of Sheffield, Department of Obstetrics and Gynaecology