Myth and reality of the decline in semen quality: an example of the relativity of data interpretation.

Many hypotheses have been put forward to explain a suspected decline in semen quality. Up to now many sources of data were used but conflicting results are present in the literature. To study whether modifications of sperm parameters actually exist we used data from two groups of patients checked and two small groups of sperm bank donors selected at the beginning '80s and '90s. We tried to reduce bias to a minimum: all the semen analyses were carried out by the same biologist, using the same methods, groups were clinically evaluated by the same andrological team, the study groups were homogeneous for age, geographic-ethnic origin, residence, monthly-seasonal distribution and abstinence period. Comparing patients from the '80s and the '90s, sperm concentration and motility showed a significant reduction. Furthermore, the decrease in concentration and motility was mainly due to the higher age classes. In donors, no decline was observed. These results seem to indicate that sperm donors remain unaffected, while patients with lower levels of semen quality are experiencing a real decline. Unfortunately, many confounding variables, analyzed in detail in this review, still remain despite efforts at standardization.