Introduction For years concerns have been raised that male semen quality is declining globally, and that this is a birth cohort effect. However, there has been a degree of subject selection bias and trend estimates have been ecological. Our study aimed to examine semen quality in a representative sample of a general population (Scottish), and to explore trend by birth year within the data.
Methods A randomly selected sample of 22–32 year-old Scottish-born men were recruited to a survey of male reproductive health. Background information was collected by questionnaire and men were asked to provide a semen sample for analysis.
Results Semen assessments were obtained for 502 men. This group was representative of the general population regarding social class, education and geography. The median sperm concentration of samples was 48×106/ml, but after adjustment to a mean abstinence of 4 days, 64×106/ml. In these adjusted data, “low” sperm counts (below 20×106/ml) were found in 18% of men (95% CI 15% to 21%). However, the prevalence of “low” sperm counts showed no trend across the 10-year range of birth years.
Conclusion This first report of sperm concentration in a random sample of a general population shows that nearly a fifth of men had poor semen quality. Further work is required to clarify the fertility relevance of a single low sperm concentration when there is no imposition of abstinence prior to sample, and to understand cause of the fertility deficit found in many survey participants.
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