Evidence of deteriorating semen quality in the United Kingdom: birth cohort study in 577 men in Scotland over 11 years

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Abstract
Objective: To determine whether the quality of semen has changed in a group of over 500 Scottish men born between 1951 and 1973. Design: Retrospective review of data on semen quality collected in a single laboratory over 11 years and according to World Health Organisation guidelines. Setting: Programme of gamete biology research funded by Medical Research Council. Subjects: 577 volunteer semen donors. Of these, 171 were born before 1959, 120 were born in 1960-4, 171 in 1965-9, and 115 in 1970-4. Main outcome measures: Conventional criteria of semen quality including semen volume (ml), sperm concentration (106/ml), overall motility (% motile), total number of sperm in the ejaculate (106), and total number of motile sperm in the ejaculate (106). Results: When the four birth cohort groups were compared a later year of birth was associated with a lower sperm concentration, a lower total number of sperm in the ejaculate, and a lower number of motile sperm in the ejaculate. The median sperm concentration fell from 98x106/ml among donors born before 1959 to 78x106/ml among donors born after 1970 (P=0.002). The total number of sperm in the ejaculate fell from 301x106 to 214x106 (P=0.0005), and the total number of motile sperm in the ejaculate fell from 169.7x106 to 129.0x106 (P=0.0065). Conclusion: This study provides direct evidence that semen quality is deteriorating, with a later year of birth being significantly associated with a reduced number of sperm in adult life. Key messages When men born in the 1970s were compared with men born in the 1950s, the total number of motile sperm in the ejaculate was reduced by almost 25% These data confirm previously published data from other countries that semen quality is changing, declining by about 2.1% per year Research is urgently required to examine the function as well as the number of sperm and to assess whether these changes are affecting human health and male fertility