Epidemiological evaluation on male reproductive function.

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1. Critical review of epidemiological evidence on changes in semen qualityWe evaluated reports on changes in semen quality published on medical journals since 1992 to see whether semen quality has been deteriorated or not over time. As a result, some reported decline in semen quality, but others reported as unchanged. Geographical and seasonal variations as well as measurement error may largely contribute to changes in semen quality. Therefore, with critical review of recent epidemiological studies, we could not conclude that semen quality has been deteriorated over time.2. Analysis of changes in semen quality of Japanese semen donor samplesWe analyzed 10906 semen quality data from 325 Japanese semen donors who visited infertility clinic in Tokyo in 1990-1998. A regression coefficient for semen concentration (all data) was-1.16 x 106/ml/year, which might indicate that semen concentration has been declined over time. However, similar analysis with the first sample of each donor only, a regression coefficient for semen concentration was not statistically significant. Additional analysis with median value of first 6 months for each also failed to show significant results. Thus, we conclude that we could not observe significant decline in semen concentration of Japanese semen donors in 1990-98.