title: Seasonal variation of semen quality and fertility.
abstract: At many locations in the northern hemisphere human sperm counts are reduced during the summer. Experiments with rhesus monkeys suggest that such seasonal variation may be induced by an endogenous biological clock reset annually by changes in the length of daylight. Little is known about seasonal variation in human female reproductive function, although fecundity may be lower during the summer, as it is for men. Variation in fecundity could help explain seasonal patterns of birth in countries such as the United States, where there is a deficit of spring births. But the relationship to patterns of birth in Canada and Europe, where the birth rate is highest during late winter and spring, is unclear.
authors.affiliation: Division of Epidemiology, Statistics, and Prevention Research, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-7510, USA. RL44W@NIH.GOV
authors.forename: R J
authors.initials: RJ
authors.lastname: Levine
mesh_terms: D000818:Animals; D005260:Female; D005298:Fertility / Q000502:physiology*; D006801:Humans; D008253:Macaca mulatta; D008297:Male; D011247:Pregnancy; D012621:Seasons; D012661:Semen / Q000502:physiology*; D013076:Sperm Count; D013081:Sperm Motility