title: Multiple-birth risk associated with IVF and extended embryo culture: USA, 2001.
abstract: BACKGROUND
  Multiple births are associated with serious adverse infant and maternal outcomes. The objective of this study was to assess the multiple-birth risk (MBR) associated with IVF and determine whether the risk is impacted by stage of embryo development at transfer.
  
  
  METHODS
  A population-based sample of 50 819 IVF transfers utilizing day 3 or day 5 embryos performed in the USA in 2001 on women aged 20-40 years was used to assess MBR and live-birth rate (LBR), stratified by patient age, supernumerary embryo availability, and number of embryos transferred.
  
  
  RESULTS
  Although significantly more day 5 than day 3 transfers used < or =2 embryos (69.2 versus 27.7%), the former were not associated with decreased MBR. MBR was high when >1 embryo was transferred, irrespective of embryo development stage. LBR were generally maximized with 2 embryos transferred, and for some (day 5 transfers, patients aged 35-37 years) with one embryo. Electing to transfer a single day 5 embryo appeared efficacious for some patients: women aged 20-37 years with supernumerary embryos cryopreserved had LBR of 31.6-39.5%.
  
  
  CONCLUSIONS
  MBR is high when > or =2 embryos are transferred. Single embryo transfer is the only way to prevent many multiple births and associated adverse health outcomes.
authors.affiliation: Epidemic Intelligence Service, Epidemiology Program Office, Division of Reproductive Health, Centers for Disease Control and Prevention, Atlanta, GA 30341-3724, USA. DKissin@cdc.gov
authors.forename: D M
authors.initials: DM
authors.lastname: Kissin
authors.forename: L A
authors.initials: LA
authors.lastname: Schieve
authors.forename: M A
authors.initials: MA
authors.lastname: Reynolds
mesh_terms: D000328:Adult; D046149:Embryo Culture Techniques / Q000706:statistics & numerical data*; D004624:Embryo Transfer / Q000706:statistics & numerical data*; D005260:Female; D005307:Fertilization in Vitro / Q000706:statistics & numerical data*; D006801:Humans; D009099:Multiple Birth Offspring / Q000706:statistics & numerical data*; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000453:epidemiology*; D012307:Risk Factors; D014481:United States / Q000453:epidemiology