title: Defining infertility--a systematic review of prevalence studies.
abstract: BACKGROUND
  Existing definitions of infertility lack uniformity, rendering comparisons in prevalence between countries or over time problematic. The absence of an agreed definition also compromises clinical management and undermines the impact of research findings. The aim of this study was to perform a systematic review of the literature to determine how infertility has been defined in prevalence studies and to come up with suggestions for a feasible and clinically relevant definition.
  
  
  METHODS
  MEDLINE, EMBASE, CINAHL and Cochrane Database of Systematic Reviews were searched for relevant population-based prevalence studies published between 1975 and 2010.
  
  
  RESULTS
  A total of 39 articles were included in the current review. The results highlight the heterogeneity of criteria used to define infertility and critical differences between demographic and epidemiological definitions. Demographers tend to define infertility as childlessness in a population of women of reproductive age, while the epidemiological definition is based on 'trying for' or 'time to' a pregnancy, generally in a population of women exposed to the risk of conception. There is considerable variation in terms of the duration of 'trying for pregnancy', the age of women sampled and their marital or cohabitation status. This leads to inconsistencies in determining the numerator and denominator used to calculate the prevalence of infertility.
  
  
  CONCLUSIONS
  There is a need for an agreed definition for infertility. We suggest a clinically relevant definition based on the duration of trying for pregnancy coupled with female age.
authors.affiliation: Obstetrics and Gynaecology, School of Medicine and Dentistry, University of Aberdeen, Aberdeen, UK.
authors.forename: S
authors.initials: S
authors.lastname: Gurunath
authors.forename: Z
authors.initials: Z
authors.lastname: Pandian
authors.forename: Richard A
authors.initials: RA
authors.lastname: Anderson
authors.forename: Siladitya
authors.initials: S
authors.lastname: Bhattacharya
mesh_terms: D000367:Age Factors; D003430:Cross-Sectional Studies; D006801:Humans; D007246:Infertility / Q000453:epidemiology*; D015995:Prevalence; D009626:Terminology as Topic; D013997:Time Factors