BACKGROUND: There is circumstantial evidence that @entity1 sperm count may have declined during past decades. The purpose of this study was to identify the association between semen quality and year of birth. METHODS: The study comprised 8608 @entity1 consulting four Danish medical centres from 1968 to 1992 because of @entity249 . Data on semen quality and @entity790 were obtained from medical records while lifestyle data were collected from a subset of the population by a postal questionnaire (response 80%). Semen characteristics were analysed as a linear function of year of birth, centre, season and calendar year at time of semen examination, sexual abstinence and lifestyle factors. Effects of age were accounted for by restriction and stratified analysis. RESULTS: The sperm count declined with increasing year of birth at two of the four centres, but this association disappeared when confounders were adjusted for. Within the subset of @entity1 born 1950-1970 we revealed a decrease in the average sperm count by 1.9 mill/ml (95% confidence interval [CI]: 1.45, 2.27) per one advancing year of birth. This finding was consistent across centres even after adjustment for effects of covariates. The proportion of morphologically normal sperm cells changed in parallel with the sperm count, while semen volume did not decline in any time periods. CONCLUSIONS: We found a birth cohort effect on sperm count and morphology among Danish infertile @entity1 born after 1950 but not in @entity1 born in the first part of the century. The findings are compatible with an environmental impact during prenatal life but the evidence is far from unequivocal.

Is semen quality related to the year of birth among Danish XXXX clients?

@entity1 :: ('9606', 'Species') :: ['human', 'men'] @entity249 :: ('MESH:D007246', 'Disease') :: ['infertility'] @entity790 :: ('MESH:D014564', 'Disease') :: ['urogenital disorders']
@entity249 :: (MESH:D007246,Disease) :: ['infertility']
