Spatiotemporal trends in human semen quality.

Linear regression analysis showed a marginally significant decrease in seminal volume between 1940 and 1990 from 3.40 ml to 2.75 ml with an estimated regression coefficient of −0.013 ml per year ( P = 0.027) and a significant decrease in mean sperm concentration weighted by number of individuals in each publication between 1940 and 1990, from 113 × 10 6 /ml to 66 × 10 6 /ml; the estimated regression coefficient was −0.934 × 10 6 /ml per year ( P < 00001).

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A decreasing trend of 0.05 ml in seminal volume was observed over the period, alongside a tendency towards reduction in sperm concentration by 1 × 10 6 /ml over the 7.5 years (mean of 34.3 × 10 6 /ml).

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In fact, 29% of all studies reported no change and 12% indicated an increasing trend.

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