Since Carlsen and co-workers reported in 1992 that sperm counts have decreased during the second half of the last century in Western societies, there has been widespread anxiety about the adverse effects of environmental pollutants on human fecundity. The Carlsen report was followed by several re-analyses of their data set and by many studies on time trends in sperm quality and on secular trends in fecundity. However, the Results of these studies were diverse, complex, difficult to interpret and, therefore, less straightforward than the Carlsen report suggested. The claims that population fecundity is declining and that environmental pollutants are involved, can neither be confirmed nor rejected, in our opinion. However, it is of great importance to find out because the possible influence of widespread environmental pollution, which would adversely affect human reproduction, should be a matter of great concern triggering large-scale studies into its causes and possibilities for prevention. The fundamental reason we still do not know whether population fecundity is declining is the lack of an appropriate surveillance system. Is such a system possible? In our opinion, determining total sperm counts (as a measure of male reproductive health) in combination with time to pregnancy (as a measure of couple fecundity) in carefully selected populations is a feasible option for such a monitoring system. If we want to find out whether or not population fecundity will be declining within the following 20-30 years, we must start monitoring now.

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Keywords Environmental effects, Epidemiology, Male infertility, Sperm quality
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te Velde, E.R., Burdorf, A., Nieschlag, E., Eijkemans, M.J.C., Kremer, J.A.M., Roeleveld, N., & Habbema, J.D.F.. (2010). Is human fecundity declining in Western countries?. Human Reproduction, 25(6), 1348–1353. doi:10.1093/humrep/deq085