title: The impact of the increasing number of multiple births on the rates of preterm birth and low birthweight: an international study.
abstract: OBJECTIVE
  We studied the effects of twins and triplets on perinatal health indicators in the overall population in the 1980s and 1990s in Canada, England and Wales, France, and the United States.
  
  
  METHODS
  Data were derived mostly from live birth registration. We used rates, relative risks, and population attributable risks for twins and triplets separately.
  
  
  RESULTS
  In each country, the increase in multiple births, and the increase in preterm delivery among multiple births, contributed almost equally to the rise in or stabilization of the overall rates of preterm delivery. Twins contributed a much larger proportion of the preterm deliveries and low-birthweight newborns than did triplets.
  
  
  CONCLUSIONS
  Twins have a major population-based impact on the trends of perinatal health indicators.
authors.affiliation: Epidemiological Research Unit on Perinatal Health and Women's Health, National Institute for Health and Medical Research, Villejuif, France. blondel@vjf.inserm.fr
authors.forename: Béatrice
authors.initials: B
authors.lastname: Blondel
authors.forename: Michael D
authors.initials: MD
authors.lastname: Kogan
authors.forename: Greg R
authors.initials: GR
authors.lastname: Alexander
authors.forename: Nirupa
authors.initials: N
authors.lastname: Dattani
authors.forename: Michael S
authors.initials: MS
authors.lastname: Kramer
authors.forename: Alison
authors.initials: A
authors.lastname: Macfarlane
authors.forename: Shi Wu
authors.initials: SW
authors.lastname: Wen
mesh_terms: D002170:Canada / Q000453:epidemiology; D003431:Cross-Cultural Comparison; D004739:England / Q000453:epidemiology; D005260:Female; D005602:France / Q000453:epidemiology; D006306:Health Surveys; D006801:Humans; D015994:Incidence; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D007752:Obstetric Labor, Premature / Q000453:epidemiology*; D011247:Pregnancy; D012307:Risk Factors; D014310:Triplets / Q000706:statistics & numerical data*; D014427:Twins / Q000706:statistics & numerical data*; D014481:United States / Q000453:epidemiology; D014852:Wales / Q000453:epidemiology