Objective-To investigate whether semen quality has changed during the past 50 years.Design-Review of publications on semen quality in men without a history of infertility selected by means of Cumulated Index Medicus and Current List (1930-1965) and MEDLINE Silver Platter database (1966( -August 1991.Subjects-14947 men included in a total of 61 papers published between 1938 and 1991.Main outcome measures-Mean sperm density and mean seminal volume.Results-Linear regression of data weighted by number of men in each study showed a significant decrease in mean sperm count from 113 x 106/ml in 1940 to 66x 106/ml in 1990 (p<0-0001) and in seminal volume from 3*40 ml to 2-75 ml (p=0.027), indicating an even more pronounced decrease in sperm production than expressed by the decline in sperm density.Conclusions-There has been a genuine decline in semen quality over the past 50 years. As male fertility is to some extent correlated with sperm count the results may reflect an overall reduction in male fertility. The biological significance ofthese changes is emphasised by a concomitant increase in the incidence of genitourinary abnormalities such as testicular cancer and possibly also cryptorchidism and hypospadias, suggesting a growing impact of factors with serious effects on male gonadal function.

Objective-To investigate whether semen quality has changed during the past 50 years.Design-Review of publications on semen quality in men without a history of infertility selected by means of Cumulated Index Medicus and Current List (1930-1965) and MEDLINE Silver Platter database (1966( -August 1991.Subjects-14947 men included in a total of 61 papers published between 1938 and 1991.Main outcome measures-Mean sperm density and mean seminal volume.Results-Linear regression of data weighted by number of men in each study showed a significant decrease in mean sperm count from 113 x 106/ml in 1940 to 66x 106/ml in 1990 (p<0-0001) and in seminal volume from 3*40 ml to 2-75 ml (p=0.027), indicating an even more pronounced decrease in sperm production than expressed by the decline in sperm density.Conclusions-There has been a genuine decline in semen quality over the past 50 years. As male fertility is to some extent correlated with sperm count the results may reflect an overall reduction in male fertility. The biological significance ofthese changes is emphasised by a concomitant increase in the incidence of genitourinary abnormalities such as testicular cancer and possibly also cryptorchidism and hypospadias, suggesting a growing impact of factors with serious effects on male gonadal function.

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It is believed that the men examined were representative of the normal population of young men in all four countries as they were recruited from groups attending a compulsory medical examination, and not selected for known fertility or semen quality. Moreover, the majority of participants had no prior knowledge of their fertility potential. It appears that an east-west gradient exists in the Nordic-Baltic area with regard to semen parameters, this being in parallel with the incidences of testicular cancer. Further investigations are required to determine whether these findings are due to genetic differences, to different environments, or perhaps to a combination of both factors.

ObjectivesConsiderable interest and controversy over a possible decline in semen quality during the 20th century raised concern that semen quality could have reached a critically low level where it might affect human reproduction. The authors therefore initiated a study to assess reproductive health in men from the general population and to monitor changes in semen quality over time.DesignCross-sectional study of men from the general Danish population. Inclusion criteria were place of residence in the Copenhagen area, and both the man and his mother being born and raised in Denmark. Men with severe or chronic diseases were not included.SettingDanish one-centre study.Participants4867 men, median age 19 years, included from 1996 to 2010.Outcome measuresSemen volume, sperm concentration, total sperm count, sperm motility and sperm morphology.ResultsOnly 23% of participants had optimal sperm concentration and sperm morphology. Comparing with historic data of men attending a Copenhagen infertility clinic in the 1940s and men who recently became fathers, these two groups had significantly better semen quality than our study group from the general population. Over the 15 years, median sperm concentration increased from 43 to 48 million/ml (p=0.02) and total sperm count from 132 to 151 million (p=0.001). The median percentage of motile spermatozoa and abnormal spermatozoa were 68% and 93%, and did not change during the study period.ConclusionsThis large prospective study of semen quality among young men of the general population showed an increasing trend in sperm concentration and total sperm count. However, only one in four men had optimal semen quality. In addition, one in four will most likely face a prolonged waiting time to pregnancy if they in the future want to father a child and another 15% are at risk of the need of fertility treatment. Thus, reduced semen quality seems so frequent that it may impair the fertility rates and further increase the demand for assisted reproduction.

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Summary The decreasing trends in fertility rates in many industrialized countries are now so dramatic that they deserve much more scientific attention. Although social and behavioural factors undoubtedly play a major role for these trends, it seems premature, and not based on solid information, to conclude that these trends can be ascribed to social and behavioural changes alone. There is evidence to suspect that changing lifestyle and increasing environmental exposures, e.g. to endocrine disrupters, are behind the trends in occurrence of male reproductive health problems, including testis cancer, undescended testis and poor semen quality. These biological factors may also contribute to the extremely low fertility rates. However, the necessary research is complex and requires non-traditional collaboration between demographers, epidemiologists, clinicians, biologists, wild life researchers, geneticists and molecular biologists. This research effort can hardly be carried out without major support from governments and granting agencies making it possible to fund collaborative projects within novel research networks of scientists.

Objective-To investigate whether semen quality has changed during the past 50 years.Design-Review of publications on semen quality in men without a history of infertility selected by means of Cumulated Index Medicus and Current List (1930-1965) and MEDLINE Silver Platter database (1966( -August 1991.Subjects-14947 men included in a total of 61 papers published between 1938 and 1991.Main outcome measures-Mean sperm density and mean seminal volume.Results-Linear regression of data weighted by number of men in each study showed a significant decrease in mean sperm count from 113 x 106/ml in 1940 to 66x 106/ml in 1990 (p<0-0001) and in seminal volume from 3*40 ml to 2-75 ml (p=0.027), indicating an even more pronounced decrease in sperm production than expressed by the decline in sperm density.Conclusions-There has been a genuine decline in semen quality over the past 50 years. As male fertility is to some extent correlated with sperm count the results may reflect an overall reduction in male fertility. The biological significance ofthese changes is emphasised by a concomitant increase in the incidence of genitourinary abnormalities such as testicular cancer and possibly also cryptorchidism and hypospadias, suggesting a growing impact of factors with serious effects on male gonadal function.