title: Temporal Trends in Fertility Rates: A Nationwide Registry Based Study from 1901 to 2014.
abstract: OBJECTIVE
  Increasing age at first childbirth has been suggested to increase the risk for infertility. Our objective is to determine whether women above thirty years of age historically have been able to sustain fertility rates above replacement level.
  
  
  METHODS
  A descriptive nationwide Danish study using birth registries from 1901-2014.
  
  
  METHODS
  Information on women's age at childbirth was obtained by using records from primary, secondary and tertiary institutions.
  
  
  METHODS
  Mothers to 8,024,969 live births.
  
  
  METHODS
  Mothers were stratified according to age at childbirth to determine total and age specific fertility rates.
  
  
  RESULTS
  Total fertility rate (TFR) decreased from 4.1 to 1.8 children per woman and age specific fertility also decreased from 1901 to 2014. Women aged 30-34, 35-39 or 40-44 years in the first decade of the 20th century had higher fertility rates than the corresponding five year younger age groups (25-29, 30-34 and 35-39, respectively) have had for the last 65 years. On average, women gave birth to two children after the age of 30 and one or more child after 35 years of age in the beginning of the 1900s. Furthermore, women more than 40 years of age accounted for 10% of TFR in 1901 compared with 4% in 2014 despite usage of assisted reproduction.
  
  
  CONCLUSIONS
  This nationwide study shows that women above 30 years of age historically have been able to sustain fertility rates above replacement level. This implies that other factors besides age are strong determinants of fertility in women above 30 years of age.
authors.affiliation: Department of Oral Medicine, Infection and Immunity, Harvard School of Dental Medicine, Boston, MA, United States of America.|Department of Growth and Reproduction and International Research and Research Training Centre in Endocrine Disruption of Male Reproduction and Child Health (EDMaRC), Rigshospitalet, Faculty of Medical and Health Sciences, University of Copenhagen, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
authors.forename: Martin
authors.initials: M
authors.lastname: Blomberg Jensen
authors.affiliation: Department of Growth and Reproduction and International Research and Research Training Centre in Endocrine Disruption of Male Reproduction and Child Health (EDMaRC), Rigshospitalet, Faculty of Medical and Health Sciences, University of Copenhagen, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
authors.forename: Lærke
authors.initials: L
authors.lastname: Priskorn
authors.affiliation: Department of Growth and Reproduction and International Research and Research Training Centre in Endocrine Disruption of Male Reproduction and Child Health (EDMaRC), Rigshospitalet, Faculty of Medical and Health Sciences, University of Copenhagen, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
authors.forename: Tina Kold
authors.initials: TK
authors.lastname: Jensen
authors.affiliation: Department of Growth and Reproduction and International Research and Research Training Centre in Endocrine Disruption of Male Reproduction and Child Health (EDMaRC), Rigshospitalet, Faculty of Medical and Health Sciences, University of Copenhagen, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
authors.forename: Anders
authors.initials: A
authors.lastname: Juul
authors.affiliation: Department of Growth and Reproduction and International Research and Research Training Centre in Endocrine Disruption of Male Reproduction and Child Health (EDMaRC), Rigshospitalet, Faculty of Medical and Health Sciences, University of Copenhagen, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
authors.forename: Niels Erik
authors.initials: NE
authors.lastname: Skakkebaek
mesh_terms: D000328:Adult; D000375:Aging / Q000502:physiology; D001723:Birth Rate / Q000639:trends*; D003718:Denmark; D005260:Female; D006801:Humans; D008875:Middle Aged; D011247:Pregnancy; D012042:Registries; D013997:Time Factors; D055815:Young Adult