[Evolution of male fertility in the last twenty years]

After the meta-analysis by Carlsen et al. (1992) showing a decline in human sperm count over the last 50 years, several studies have been made on the sperm characteristics of more or less homogeneous groups of men who were collecting semen in the same center for 10-20 years. A significant decline in sperm count was reported in some studies but not in others. The debate on declining sperm counts is not closed and these studies raised the following important questions: could the differences in results be the reflect of variation in techniques or blas in methodologies? If these phenomena are real, why a deterioration of semen quality in some places and not in others with so important geographical differences of sperm production? What are the possible consequences on human fertility and what are the causes? Unfortunately, there is presently no answer. The danish study provoked extensive discussion on the many possible sources of bias while there was less controversy concerning the studies carried out in a single center despite the extent of limitations of several of them. Recent publications indicated concomitant and increasing alterations of the development and/or function of the male genital tract, various observations in the wildlife and several experimental studies suggesting the possible deleterious role of numerous chemical compounds present in our environment. Therefore, prospective epidemiological studies and fundamental researchs are urgently needed.