title: The effect of two distinct levels of oxygen concentration on embryo development in a sibling oocyte study.
abstract: OBJECTIVE
  This prospective randomized study used sibling oocytes of 258 women with ≥8 oocytes to compare the effect of 5 % O(2) versus 20 % O(2) concentrations on embryo development and clinical outcome.
  
  
  METHODS
  Oocytes of each case were divided between incubators with either 5 % or 20 % O(2) concentration. Outcome measures were fertilization, cleavage, embryo quality, blastocyst formation, and implantation, pregnancy and live birth rates.
  
  
  RESULTS
  Fertilization and cleavage rates were similar in both groups. The 5 % O(2) group had significantly more blastomeres (P < 0.05) and more top-quality embryos on day 3 (P < 0.02), as well as significantly more available embryos for transfer (31.6 % vs. 23.1 % for the 20 % O(2) group; P < 0.0001). There were significantly more cycles with good embryos in the 5 % group (76/258) than in the 20 % group (38/258) (P < 0.0001). Implantation and pregnancy rates were significantly higher for 5 % O(2) embryos (P < 0.03 and P < 0.05, respectively). Live birth rates per embryo transfer were 34.2 % and 15.8 %, respectively, P < 0.05.
  
  
  CONCLUSIONS
  Implantation, pregnancy and live birth rates are higher, and more good quality embryos are available for transfer and freezing with reduced rather than with atmospheric oxygen concentrations during embryo incubation.
authors.affiliation: Infertility and IVF Unit, Assaf Harofeh Medical Center, Zerifin, 70300, Israel, ekasterstein@gmail.com.
authors.forename: Esti
authors.initials: E
authors.lastname: Kasterstein
authors.forename: Deborah
authors.initials: D
authors.lastname: Strassburger
authors.forename: Daphna
authors.initials: D
authors.lastname: Komarovsky
authors.forename: Orna
authors.initials: O
authors.lastname: Bern
authors.forename: Alisa
authors.initials: A
authors.lastname: Komsky
authors.forename: Arieh
authors.initials: A
authors.lastname: Raziel
authors.forename: Shevach
authors.initials: S
authors.lastname: Friedler
authors.forename: Raphael
authors.initials: R
authors.lastname: Ron-El
mesh_terms: D000328:Adult; D015925:Cryopreservation; D046149:Embryo Culture Techniques; D010064:Embryo Implantation; D004624:Embryo Transfer; D047108:Embryonic Development / Q000187:drug effects*; D005260:Female; D006801:Humans; D054315:Oocyte Retrieval; D009865:Oocytes / Q000254:growth & development; D010100:Oxygen / Q000494:pharmacology*; D011247:Pregnancy; D011256:Pregnancy Outcome; D018873:Pregnancy Rate; D020554:Sperm Injections, Intracytoplasmic
chemical_list: D010100:Oxygen