title: Clinical effectiveness of elective single versus double embryo transfer: meta-analysis of individual patient data from randomised trials.
abstract: OBJECTIVE
  To compare the effectiveness of elective single embryo transfer versus double embryo transfer on the outcomes of live birth, multiple live birth, miscarriage, preterm birth, term singleton birth, and low birth weight after fresh embryo transfer, and on the outcomes of cumulative live birth and multiple live birth after fresh and frozen embryo transfers.
  
  
  METHODS
  One stage meta-analysis of individual patient data.
  
  
  METHODS
  A systematic review of English and non-English articles from Medline, Embase, and the Cochrane Central Register of Controlled Trials (up to 2008). Additional studies were identified by contact with clinical experts and searches of bibliographies of all relevant primary articles. Search terms included embryo transfer, randomised controlled trial, controlled clinical trial, single embryo transfer, and double embryo transfer. Review methods Comparisons of the clinical effectiveness of cleavage stage (day 2 or 3) elective single versus double embryo transfer after fresh or frozen in vitro fertilisation (IVF) or intracytoplasmic sperm injection (ICSI) treatments were included. Trials were included if the intervention differed only in terms of the intended number of embryos to be transferred. Trials that involved only blastocyst (day five) transfers were excluded.
  
  
  RESULTS
  Individual patient data were received for every patient recruited to all eight eligible trials (n=1367). A total of 683 and 684 women randomised to the single and double embryo transfer arms, respectively, were included in the analysis. Baseline characteristics in the two groups were comparable. The overall live birth rate in a fresh IVF cycle was lower after single (181/683, 27%) than double embryo transfer (285/683, 42%) (adjusted odds ratio 0.50, 95% confidence interval 0.39 to 0.63), as was the multiple birth rate (3/181 (2%) v 84/285 (29%)) (0.04, 0.01 to 0.12). An additional frozen single embryo transfer, however, resulted in a cumulative live birth rate not significantly lower than the rate after one fresh double embryo transfer (132/350 (38%) v 149/353 (42%) (0.85, 0.62 to 1.15), with a minimal cumulative risk of multiple birth (1/132 (1%) v 47/149 (32%)). The odds of a term singleton birth (that is, over 37 weeks) after elective single embryo transfer was almost five times higher than the odds after double embryo transfer (4.93, 2.98 to 8.18).
  
  
  CONCLUSIONS
  Elective single embryo transfer results in a higher chance of delivering a term singleton live birth compared with double embryo transfer. Although this strategy yields a lower pregnancy rate than a double embryo transfer in a fresh IVF cycle, this difference is almost completely overcome by an additional frozen single embryo transfer cycle. The multiple pregnancy rate after elective single embryo transfer is comparable with that observed in spontaneous pregnancies.
authors.affiliation: Medical Statistics Team, Section of Population Health, University of Aberdeen, Aberdeen AB25 2ZD, UK. d.mclernon@abdn.ac.uk
authors.forename: D J
authors.initials: DJ
authors.lastname: McLernon
authors.forename: K
authors.initials: K
authors.lastname: Harrild
authors.forename: C
authors.initials: C
authors.lastname: Bergh
authors.forename: M J
authors.initials: MJ
authors.lastname: Davies
authors.forename: D
authors.initials: D
authors.lastname: de Neubourg
authors.forename: J C M
authors.initials: JC
authors.lastname: Dumoulin
authors.forename: J
authors.initials: J
authors.lastname: Gerris
authors.forename: J A M
authors.initials: JA
authors.lastname: Kremer
authors.forename: H
authors.initials: H
authors.lastname: Martikainen
authors.forename: B W
authors.initials: BW
authors.lastname: Mol
authors.forename: R J
authors.initials: RJ
authors.lastname: Norman
authors.forename: A
authors.initials: A
authors.lastname: Thurin-Kjellberg
authors.forename: A
authors.initials: A
authors.lastname: Tiitinen
authors.forename: A P A
authors.initials: AP
authors.lastname: van Montfoort
authors.forename: A M
authors.initials: AM
authors.lastname: van Peperstraten
authors.forename: E
authors.initials: E
authors.lastname: Van Royen
authors.forename: S
authors.initials: S
authors.lastname: Bhattacharya
mesh_terms: D000022:Abortion, Spontaneous; D000328:Adult; D004624:Embryo Transfer / Q000379:methods*; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D050498:Live Birth; D008423:Maternal Age; D011247:Pregnancy; D018873:Pregnancy Rate; D011272:Pregnancy, Multiple / Q000706:statistics & numerical data; D016032:Randomized Controlled Trials as Topic