title: Consistent age-dependent declines in human semen quality: a systematic review and meta-analysis.
abstract: Reduced fertility typically occurs among women in their late 30s, but increasing evidence indicates that advanced paternal age is associated with changes in reproduction as well. Numerous studies have investigated age-based declines in semen traits, but the impact of paternal age on semen parameter values remains inconclusive. Using data from 90 studies (93,839 subjects), we conducted a systematic review and meta-analysis to quantify the effect of male age on seven ejaculate traits (semen volume, sperm concentration, total sperm count, morphology, total motility, progressive motility and DNA fragmentation). Age-associated declines in semen volume, percentage motility, progressive motility, normal morphology and unfragmented cells were statistically significant and results generally seemed to be robust against confounding factors. Unexpectedly, sperm concentration did not decline with increasing male age, even though we found that sperm concentration declined over time. Our findings indicate that male age needs more recognition as a potential contributor to the negative pregnancy outcomes and reduced offspring health associated with delayed first reproduction. We suggest that greater focus on collection of DNA fragmentation and progressive motility in a clinical setting may lead to better patient outcomes during fertility treatments of aging couples.
authors.affiliation: Department of Anatomy, University of Otago, Dunedin 9054, New Zealand; Department of Zoology, University of Otago, Dunedin 9054, New Zealand; Allan Wilson Centre, University of Otago, Dunedin 9054, New Zealand. Electronic address: sheri.johnson@otago.ac.nz.
authors.forename: Sheri L
authors.initials: SL
authors.lastname: Johnson
authors.affiliation: Department of Anatomy, University of Otago, Dunedin 9054, New Zealand.
authors.forename: Jessica
authors.initials: J
authors.lastname: Dunleavy
authors.affiliation: Department of Anatomy, University of Otago, Dunedin 9054, New Zealand; Allan Wilson Centre, University of Otago, Dunedin 9054, New Zealand; Gravida: National Centre for Growth and Development, University of Otago, Dunedin 9054, New Zealand.
authors.forename: Neil J
authors.initials: NJ
authors.lastname: Gemmell
authors.affiliation: Department of Zoology, University of Otago, Dunedin 9054, New Zealand; Gravida: National Centre for Growth and Development, University of Otago, Dunedin 9054, New Zealand.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Nakagawa
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012661:Semen / Q000502:physiology; D055101:Semen Analysis; D013076:Sperm Count; D013094:Spermatozoa / Q000502:physiology; D055815:Young Adult
keywords: Fertility; Male aging; Meta-regression; Paternal age; Quantitative synthesis; Sperm performance