title: Semen quality in the 21stcentury.
abstract: Although semen quality is an important determinant of fertility, defining clear thresholds for normal ranges has proven difficult. According to 'time to pregnancy' studies, fecundity starts to decline when sperm concentrations fall below 30-55 × 106/ml, whereas the WHO criterion for normal values is currently 15 × 106/ml. Multiple studies over the past 15 years have reported median sperm concentrations of 41-55 × 106/ml in young men (mean age 18-21 years) from the general population, suggesting that many of them have suboptimal semen quality. Sperm numbers remain fairly constant between 19 and 29 years of age, which points to the importance of developmental effects. Discussion on whether population semen quality has declined has continued for decades, as regional differences in trends have been noted. The reasons for poor semen quality and adverse trends are not well established, but some associations suggest a causal relationship, for example, with maternal smoking during pregnancy. The role of chemical exposures leading to endocrine disruption and detrimental reproductive effects has been in the focus of research during the past 20 years. Identification of exposures that affect fertility could provide opportunities for effective prevention of reproductive health problems.
authors.affiliation: Department of Physiology, Institute of Biomedicine, University of Turku, Kiinamyllynkatu 10, 20520 Turku, Finland.
authors.forename: Helena E
authors.initials: HE
authors.lastname: Virtanen
authors.affiliation: University Department of Growth and Reproduction and International Center for Research and Research Training in Endocrine Disruption of Male Reproduction and Child Health (EDMaRC), Rigshospitalet, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
authors.forename: Niels
authors.initials: N
authors.lastname: Jørgensen
authors.affiliation: Department of Physiology, Institute of Biomedicine, University of Turku, Kiinamyllynkatu 10, 20520 Turku, Finland.|University Department of Growth and Reproduction and International Center for Research and Research Training in Endocrine Disruption of Male Reproduction and Child Health (EDMaRC), Rigshospitalet, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.|Department of Paediatrics, Turku University Hospital, Kiinamyllynkatu 4 - 8, PL 52, 20521 Turku, Finland.
authors.forename: Jorma
authors.initials: J
authors.lastname: Toppari
mesh_terms: D004781:Environmental Exposure / Q000009:adverse effects*; D006801:Humans; D007248:Infertility, Male / Q000175:diagnosis / Q000453:epidemiology* / Q000503:physiopathology; D038622:Internationality; D008019:Life Style; D008297:Male; D012661:Semen / Q000502:physiology*; D055101:Semen Analysis / Q000639:trends*; D013076:Sperm Count / Q000639:trends; D013081:Sperm Motility / Q000502:physiology