title: Number of embryos for transfer after IVF and ICSI: a Cochrane review.
abstract: BACKGROUND
  The most common complication of IVF is multiple pregnancy, which occurs in 25% of pregnancies following the transfer of two embryos. Single embryo transfer can minimize twin pregnancies but could also lower live birth rates. Our aim was to perform a systematic review of randomized trials to determine the effectiveness of single versus double embryo transfer.
  
  
  METHODS
  Cochrane Collaboration review methods were followed. Randomized controlled trials comparing single and double embryo transfers were identified by searching Medline, EMBASE and the Cochrane register of controlled trials. Contents of specialist journals and proceedings from meetings of relevant societies were hand searched. Data were pooled with Rev Man software using the Peto-modified Mantel-Hanzel method.
  
  
  RESULTS
  Pooled results from four trials indicate that although double embryo transfer leads to a higher live birth rate per woman [odds ratio (OR) 1.94, 95% confidence interval (CI) 1.47-2.55] in a fresh IVF cycle, comparable results are obtained by subsequent transfer of a frozen embryo (OR 1.19, 95% CI 0.87-1.62). The multiple pregnancy rate is significantly higher (OR 62.83, 95% CI 8.52-463.57) after double embryo transfer.
  
  
  CONCLUSIONS
  Single embryo transfer significantly reduces the risk of multiple pregnancy, but also decreases the chance of live birth in a fresh IVF cycle. Subsequent replacement of a single frozen embryo achieves a live birth rate comparable with double embryo transfer.
authors.affiliation: Department of Obstetrics & Gynaecology, Aberdeen Maternity Hospital, Aberdeen, UK. ogy211@abdn.ac.uk
authors.forename: Zabeena
authors.initials: Z
authors.lastname: Pandian
authors.forename: Allan
authors.initials: A
authors.lastname: Templeton
authors.forename: Gamal
authors.initials: G
authors.lastname: Serour
authors.forename: Siladitya
authors.initials: S
authors.lastname: Bhattacharya
mesh_terms: D000328:Adult; D002986:Clinical Trials as Topic; D015925:Cryopreservation; D019992:Databases as Topic; D016206:Databases, Bibliographic; D004624:Embryo Transfer; D004622:Embryo, Mammalian; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods*; D006801:Humans; D016239:MEDLINE; D009099:Multiple Birth Offspring; D016017:Odds Ratio; D011247:Pregnancy; D011256:Pregnancy Outcome; D018873:Pregnancy Rate; D011272:Pregnancy, Multiple; D016032:Randomized Controlled Trials as Topic; D027724:Reproductive Techniques, Assisted; D012984:Software; D020554:Sperm Injections, Intracytoplasmic / Q000379:methods*; D013997:Time Factors; D016896:Treatment Outcome; D014427:Twins