title: Comparison of 5% and ambient oxygen during days 3-5 of in vitro culture of human embryos.
abstract: OBJECTIVE
  To compare the effect of two oxygen concentrations used during days 3-5 of human embryo culture on embryo quality and pregnancy outcome.
  
  
  METHODS
  Retrospective analysis of the use of two culture conditions.
  
  
  METHODS
  University-based infertility clinic.
  
  
  METHODS
  Three hundred eighty-two patients undergoing IVF.
  
  
  METHODS
  Embryos were cultured in 5% CO(2) balanced ( approximately 20% O(2)) gas phase until day 3 then assigned to approximately 20% or reduced (5%) oxygen concentration groups and cultured until ET.
  
  
  METHODS
  Embryo quality, pregnancy rates, and implantation rates.
  
  
  RESULTS
  There were no differences in demographic features (age, type of infertility) between the two groups. The embryo scores at day 3 and day 5, blastulation rate, and transfer score did not differ between groups. No differences were observed between the 5% and 20% oxygen concentrations in the chemical pregnancy rate (71.27% vs. 78.72%), clinical pregnancy rate (58.56% vs. 64.36%), or implantation rate (44.06% vs. 44.16%).
  
  
  CONCLUSIONS
  Reduced oxygen concentration in the gas mixture from day 3 until ET did not support better embryo development or result in higher pregnancy or implantation rates. These data do not support the hypothesis that beneficial effects of reduced oxygen concentration can be gained by employing the strategy during the latter stages of embryo culture (days 3-5) only and highlight the need for further studies through all stages of in vitro culture.
authors.affiliation: Department of Surgery, Andrology and IVF Laboratories, University of Utah School of Medicine, Salt Lake City, Utah 84108, USA.
authors.forename: Laszlo
authors.initials: L
authors.lastname: Nanassy
authors.forename: C Anthony
authors.initials: CA
authors.lastname: Peterson
authors.forename: Aaron L
authors.initials: AL
authors.lastname: Wilcox
authors.forename: C Matthew
authors.initials: CM
authors.lastname: Peterson
authors.forename: Ahmad
authors.initials: A
authors.lastname: Hammoud
authors.forename: Douglas T
authors.initials: DT
authors.lastname: Carrell