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|  |  | | (This debate is closed and is a read-only archive.) | Toxic testes?
[19-Nov-2004]
| | 'In spite of all the scaremongering, scientists are still divided as to whether there has been any major change in semen quality across the world.' |  | | | Claims that male sperm counts have declined significantly in recent years first made the headlines in 1992. This followed the publication of a meta-analysis by Carlson and colleagues, in which they reviewed the data from 61 previously published studies and concluded that sperm counts had almost halved over the 53 years from 1938 to 1991. Although subsequently criticised for its approach, and the statistical strategy employed, this study had two significant effects.
| First, it triggered scientists and medical staff around the world to search their own databases for evidence of a local decline in semen quality among the men attending their clinic or laboratory for semen analysis. This prompted a further series of publications (and associated media publicity) in which evidence of decline in sperm counts at a variety of worldwide locations was apparently confirmed (giving support to the hypothesis), or found to be unchanged (therefore refuting it). As such, the data is tantalisingly complex for all but the specialist reader, and no wonder that journalists and some scientists are often confused by it.
| Second, these scientific publications prompted a plethora of news stories that have fuelled the popular belief that male fertility and semen quality are under serious threat from pollution or the modern lifestyle. In some reports it is even suggested that in a few years time many more couples would require infertility treatments (such as in vitro fertilisation (IVF) or intra-cytoplasmic sperm injection (ICSI) in order to reproduce. While such scaremongering is not helpful, it does put back on the agenda the debate as to whether sperm counts are actually declining, as well as the subject of male infertility that is too often overlooked.
| Over 12 years since that original publication by Carlson, scientists are still divided as to whether there has been any major change in semen quality across the world. What seems to be clear is that the factors that control and influence male fertility are unsurprisingly complex. However, too many studies rely on the analysis of retrospective (archival) data, an approach that is laudable but fraught with potential biases and confounders. For example:
| - There is increased social acceptability of infertility around the world and there has been progressively better access to infertility services in recent years. As such, the number of patients being referred for semen analysis has steadily increased year-on-year and it is not always possible to determine if the profile of patients referred for semen analysis in a given centre has remained constant over time.
- There are now better treatments available to overcome sub-fertility in men. For example, the development of ICSI has, over the past 10 years, revolutionised the ability of men with very low sperm counts to conceive their own genetic child. As such, many more sub-fertile men are attending clinics for semen analysis.
- The techniques of semen analysis have changed (and improved markedly) over the past 20 years. Although since 1980 the World Health Organisation (WHO) has published international guidelines, each subsequent edition has systematically tightened the technical aspects of laboratory technique and has outlawed the use of inadequate methods.
- An increasing awareness of the need for internal and external quality control has shown that the variation between laboratories in their ability to diagnose the semen sample is enormous, and in some instances is far greater than the perceived decline in semen quality across the world. This makes it almost impossible to compare data between different laboratories around the world.
As a consequence of these four factors (and others), progress in understanding whether the human male reproductive tract is under assault from specific chemical substances, or other aspects of modern living, has been very slow.
| So where does this leave us? The only way to answer whether semen quality of adult males may be declining is to undertake in-depth long-term prospective studies that investigate the reproductive health of men in advance of their attempts to conceive. This is important because it is now known that the fertility of the adult male may well be established as early as during neonatal life. Such approaches are not cheap and will require a significant funding. But surely now is the time to begin work so that if male fertility is under assault from unknown factors we have time to take preventative action.
| Allan Pacey is senior lecturer in andrology, University of Sheffield. He will be speaking at 'ENVIRONMENTAL AND HUMAN HEALTH EFFECTS OF ENDOCRINE DISRUPTING CHEMICALS' at the Society of Chemical Industry, Belgrave Square, London. See the Society of Chemical Industry website for further details.
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