title: Elective single-embryo transfer versus double-embryo transfer in in vitro fertilization.
abstract: BACKGROUND
  The risks of premature birth and perinatal death are increased after in vitro fertilization. These risks are mainly due to the high incidence of multiple births, which relates to the number of embryos transferred.
  
  
  METHODS
  We performed a randomized, multicenter trial to assess the equivalence of two approaches to in vitro fertilization with respect to the rates of pregnancy that result in at least one live birth and to compare associated rates of multiple gestation. Women less than 36 years of age who had at least two good-quality embryos were randomly assigned either to undergo transfer of a single fresh embryo and, if there was no live birth, subsequent transfer of a single frozen-and-thawed embryo, or to undergo a single transfer of two fresh embryos. Equivalence was defined as a difference of no more than 10 percentage points in the rates of pregnancy resulting in at least one live birth.
  
  
  RESULTS
  Pregnancy resulting in at least one live birth occurred in 142 of 331 women (42.9 percent) in the double-embryo-transfer group as compared with 128 of 330 women (38.8 percent) in the single-embryo-transfer group (difference, 4.1 percentage points; 95 percent confidence interval, -3.4 to 11.6 percentage points); rates of multiple births were 33.1 percent and 0.8 percent, respectively (P<0.001). These results do not demonstrate equivalence of the two approaches in rates of live births, but they do indicate that any reduction in the rate of live births with the transfer of single embryos is unlikely to exceed 11.6 percentage points.
  
  
  CONCLUSIONS
  In women under 36 years of age, transferring one fresh embryo and then, if needed, one frozen-and-thawed embryo dramatically reduces the rate of multiple births while achieving a rate of live births that is not substantially lower than the rate that is achievable with a double-embryo transfer.
authors.affiliation: From the Department of Obstetrics and Gynecology, Institute for Health of Women and Children, Sahlgrenska University Hospital, Göteborg, Sweden.
authors.forename: Ann
authors.initials: A
authors.lastname: Thurin
authors.forename: Jon
authors.initials: J
authors.lastname: Hausken
authors.forename: Torbjörn
authors.initials: T
authors.lastname: Hillensjö
authors.forename: Barbara
authors.initials: B
authors.lastname: Jablonowska
authors.forename: Anja
authors.initials: A
authors.lastname: Pinborg
authors.forename: Annika
authors.initials: A
authors.lastname: Strandell
authors.forename: Christina
authors.initials: C
authors.lastname: Bergh
mesh_terms: D000328:Adult; D001723:Birth Rate; D015925:Cryopreservation; D004624:Embryo Transfer; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods; D006801:Humans; D008423:Maternal Age; D009099:Multiple Birth Offspring; D011247:Pregnancy; D011256:Pregnancy Outcome; D011272:Pregnancy, Multiple; D020554:Sperm Injections, Intracytoplasmic