[Is today's man really less fertile?]

In 1992, a statistical analysis of data from 61 studies of semen quality among normal men led to the conclusion that human sperm count fell of 40% from 1940 to 1990. This meta-analysis has since been invalidated for methodological reasons as well as for statistical reasons, but it caused enormous concern to both the scientific community and to the international media. A decline of human fertility was speculated. To date, the most popular hypothesis offered to explain this alleged decline has been increasing exposure to environmental estrogen mimicking chemicals. However, there is no evidence that male or mammal fertility is declining. Moreover, the sperm count of breeding mammals did not declined in the meanwhile. Since 1992, numerous papers reported on men investigated during the last 20 years have shown conflicting results, from sperm count improvement to sperm count decline. However, several publications included methodological and analytical biases. In fact, the techniques used for semen analysis have to be questioned. It is a subjective exam, lacking laboratory standards and quality control procedures. This induces very important variations between laboratories and between biologists. For the sperm count itself, numerous errors can occur, provoked by the technique, the equipment and the reader: for the same sperm, the coefficient of variation can exceed 40% between two technicians. Therefore, the current techniques of semen analysis cannot warrant epidemiological studies. It is indispensable to admit the limits of the semen analysis in order to improve as much as possible its quality and its reliability.