title: Longitudinal changes in semen parameters in young Danish men from the Copenhagen area.
abstract: BACKGROUND
  Several recent studies have reported low sperm concentration in young men recruited from the general population, but it is unknown whether the semen quality of these young men reflects that of more mature men or is reduced due to relative immaturity. We conducted a longitudinal follow-up study to address this question.
  
  
  METHODS
  We followed 158 young men (median age = 19.1 years at entry) for up to 4 years and requested quarterly semen samples (total 1838 semen samples) and yearly genital examinations. We examined longitudinal changes in sperm concentration, semen volume, percentage of immotile sperm and percentage of morphologically normal sperm. We used general linear models in which each man served as his own control which also controlled for age, smoking, urogenital infections or disorders, fever and abstinence time.
  
  
  RESULTS
  We found no evidence that sperm concentration, total sperm count or percentage of morphologically normal sperm changed appreciably during the 4 years of follow-up. Semen volume appeared to increase slightly with age, perhaps due to greater acceptance of the study protocol by participants. Sperm motility also improved somewhat, although this may, at least in part, reflect a trend in motility measurement.
  
  
  CONCLUSIONS
  In this analysis of 1838 semen samples from 158 young men from the Copenhagen area, sperm concentration, total sperm count and sperm morphology did not change significantly during 4 years of follow-up, suggesting that previously reported low sperm concentration and poor sperm morphology among young Danish men are unlikely to be the result of immaturity.
authors.affiliation: University Department of Growth and Reproduction, GR 5064, Copenhagen University Hospital, Blegdamsvej 9, DK-2100 Copenhagen. ecarlsen@rh.dk
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Carlsen
authors.forename: Shanna H
authors.initials: SH
authors.lastname: Swan
authors.forename: Jørgen Holm
authors.initials: JH
authors.lastname: Petersen
authors.forename: Niels E
authors.initials: NE
authors.lastname: Skakkebaek
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D003718:Denmark / Q000453:epidemiology; D005334:Fever / Q000453:epidemiology; D005500:Follow-Up Studies; D005832:Genital Diseases, Male / Q000453:epidemiology; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D009845:Oligospermia / Q000453:epidemiology*; D012621:Seasons; D012661:Semen / Q000166:cytology*; D012746:Sexual Abstinence; D012741:Sexual Maturation; D013076:Sperm Count / Q000706:statistics & numerical data*; D013737:Testis / Q000033:anatomy & histology