title: Time trends in human fecundability in Sweden.
abstract: BACKGROUND
  Trends in biologic fertility are elusive. Possible negative trends in male reproductive health are still debated, and their effect on human fertility might be negligible. Time-to-pregnancy (TTP) is a functional measure of couple fecundability.
  
  
  METHODS
  We analyzed data on TTP among 832,000 primiparous women 20 years of age and older in the nationwide Swedish Medical Birth Registry from 1983 through 2002. This age restriction led to an exclusion of 10% of primiparous pregnancies. Subfertility (TTP > or =1 year) was analyzed as a function of maternal age, calendar time at initiation of attempt, and birth cohort-taking into account the truncation problems that are inherent in birth-based retrospective sampling.
  
  
  RESULTS
  Subfertility generally decreased over successive birth cohorts. When studied as a period effect, a transient increase in subfertility was seen in the early 1990s. Subfertility increased with age, except that for women in their late 1930s, an apparent decrease was observed, particularly among the early cohorts.
  
  
  CONCLUSIONS
  We found decreasing subfertility over time. We speculate that these patterns might be related to a Sweden-specific decrease over time in sexually transmitted diseases, to changes in sexual behavior induced by socioeconomic conditions, or to broader biologic or educational trends.
authors.affiliation: Department of Biostatistics, University of Copenhagen, Denmark. T.Scheike@biostat.ku.dk
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Scheike
authors.forename: Lars
authors.initials: L
authors.lastname: Rylander
authors.forename: Lisbeth
authors.initials: L
authors.lastname: Carstensen
authors.forename: Niels
authors.initials: N
authors.lastname: Keiding
authors.forename: Tina Kold
authors.initials: TK
authors.lastname: Jensen
authors.forename: Ulf
authors.initials: U
authors.lastname: Stromberg
authors.forename: Michael
authors.initials: M
authors.lastname: Joffe
authors.forename: Olof
authors.initials: O
authors.lastname: Akre
mesh_terms: D000328:Adult; D000367:Age Factors; D015988:Cohort Effect; D003710:Demography; D005260:Female; D005298:Fertility; D006801:Humans; D007407:Interviews as Topic; D008297:Male; D008423:Maternal Age; D008875:Middle Aged; D011247:Pregnancy; D018873:Pregnancy Rate / Q000639:trends*; D012042:Registries; D012044:Regression Analysis; D013548:Sweden; D013997:Time Factors