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

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 (10(6)/ml), overall motility (% motile), total number of sperm in the ejaculate (10(6)), and total number of motile sperm in the ejaculate (10(6)).

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 98x10(6)/ml among donors born before 1959 to 78x10(6)/ml among donors born after 1970 (P=0.002). The total number of sperm in the ejaculate fell from 301x10(6) to 214x10(6) (P=0.0005), and the total number of motile sperm in the ejaculate fell from 169.7x10(6) to 129.0x10(6) (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.