There have been numerous published studies that have retrospectively surveyed the occupations of men attending infertility clinics and/or compared occupations of fertile and infertile groups. There is some consensus in showing, for example, that farmers/agricultural workers or lorry drivers, painters, or welders may be overrepresented in infertile men (15,16), but overall, the findings of such studies are inconsistent and have failed to identify common occupational causes of male infertility. Occupation is only one of a range of factors that may cause male infertility, and, therefore, searching for such factors in patients at the infertility clinic may not be the most sensitive approach. However, alternative approaches, such as direct investigation of particular working groups, also have various problems (12). Low participation rates are common and may be biased toward those who have experienced, or suspect, a fertility problem (17). These make interpretation of any findings difficult. Another common problem is the low numbers of workers who may eventually comprise the exposed or control groups, because many published studies involved 30-50 men or fewer per group (12,18,19). As sperm counts and other semen parameters show great variation between subjects, detection of a workplace/occupational effect against such a background requires considerable numbers of subjects, otherwise, the study will lack sufficient power to detect anything other than a major change in semen parameters. For example, approx 80 control and exposed men would be required to detect a 20% fall in sperm count. Finally, there are likely to be many confounding factors in any occupational study. These may include age, ejaculatory frequency/abstinence, smoking and alcohol consumption, recreational drug use, time spent seated (see section on scrotal temperature), recent infection or febrile period, history of cryptorchidism, sexually transmitted disease, and so on (20). Attempts can be made to control for some of these factors, but with the generally small numbers of subjects involved, this is inevitably less than satisfactory. Against this background, it is therefore not surprising that relatively few occupations or workplace exposures have been shown consistently to impact significantly on male reproductive health (usually on sperm counts/fertility). However, there is reasonable evidence to suggest that exposure to some solvents (21), glycol ethers (22), and inorganic lead (23-25) can affect one or more aspects of semen quality in exposed workers and, in some instances, affect fertility or miscarriage rates (although effects on the latter two parameters are small). Nevertheless, other studies that showed no significant effect of similar exposures can be found in the literature (26,27). This would support the view that such workplace exposures have only minor effects on semen quality and male fertility, although in some individuals, such as those with a low sperm count for other reasons, such effects might significantly affect fertility.
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