title: Fertility treatments and multiple births in the United States.
abstract: BACKGROUND
  The advent of fertility treatments has led to an increase in the rate of multiple births in the United States. However, the trends in and magnitude of the contribution of fertility treatments to the increase are uncertain.
  
  
  METHODS
  We derived the rates of multiple births after natural conception from data on distributions of all births from 1962 through 1966 (before fertility treatments were available). Publicly available data on births from 1971 through 2011 were used to determine national multiple birth rates, and data on in vitro fertilization (IVF) from 1997 through 2011 were used to estimate the annual proportion of multiple births that were attributable to IVF and to non-IVF fertility treatments, after adjustment for maternal age. Trends in multiple births were examined starting from 1998, the year when clinical practice guidelines for IVF were developed with an aim toward reducing the incidence of multiple births.
  
  
  RESULTS
  We estimated that by 2011, a total of 36% of twin births and 77% of triplet and higher-order births resulted from conception assisted by fertility treatments. The observed incidence of twin births increased by a factor of 1.9 from 1971 to 2009. The incidence of triplet and higher-order births increased by a factor of 6.7 from 1971 to 1998 and decreased by 29% from 1998 to 2011. This decrease coincided with a 70% reduction in the transfer of three or more embryos during IVF (P<0.001) and a 33% decrease in the proportion of triplet and higher-order births attributable to IVF (P<0.001).
  
  
  CONCLUSIONS
  Over the past four decades, the increased use of fertility treatments in the United States has been associated with a substantial rise in the rate of multiple births. The rate of triplet and higher-order births has declined over the past decade in the context of a reduction in the transfer of three or more embryos during IVF. (Funded by the Centers for Disease Control and Prevention.).
authors.affiliation: From the Women's Health and Fertility Branch, Division of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, Atlanta (A.D.K., D.J.J., D.M.K., M.F.G.); the Johns Hopkins School of Medicine, Baltimore (H.W.J.); the Eastern Virginia Medical School, Norfolk (H.W.J.); the Division of Biostatistics and Epidemiology, Cincinnati Children's Hospital Medical Center, Cincinnati (M.M.); and the Warren Alpert Medical School, Brown University, Providence, RI (E.Y.A.).
authors.forename: Aniket D
authors.initials: AD
authors.lastname: Kulkarni
authors.forename: Denise J
authors.initials: DJ
authors.lastname: Jamieson
authors.forename: Howard W
authors.initials: HW
authors.lastname: Jones
authors.forename: Dmitry M
authors.initials: DM
authors.lastname: Kissin
authors.forename: Maria F
authors.initials: MF
authors.lastname: Gallo
authors.forename: Maurizio
authors.initials: M
authors.lastname: Macaluso
authors.forename: Eli Y
authors.initials: EY
authors.lastname: Adashi
mesh_terms: D000328:Adult; D004624:Embryo Transfer / Q000639:trends; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D008423:Maternal Age; D009099:Multiple Birth Offspring / Q000706:statistics & numerical data*; D011247:Pregnancy; D027724:Reproductive Techniques, Assisted / Q000639:trends; D014481:United States