Is sperm quality actually declining? A literature survey

The possible decline in human semen quality has become a recent major issue of concern. An article on a meta-analysis published by Carlsen and co-workers in 1992 claims to have shown a 50% reduction in semen quality over the last 50 years. This caused quite a stir in the media. However, the supposed decline in human sperm quality was far from unambiguous, considering the amount of criticism this article received and the contradictory results shown in other publications at the time. In a study designed to assess the likelihood of a true decline by critically analysing the Carlsen and co-workers study and the epidemiologically oriented articles describing trend in sperm parameters, the design and performance of each of the separate studies was evaluated for possible bias and confounders, and for validity of measuring methods and statistics. The evidence obtained was not convincing enough to support quantative or qualitative sperm decline over the last few decades