title: Reduced oxygen tension improves embryo quality but not clinical pregnancy rates: a randomized clinical study into ovum donation cycles.
abstract: OBJECTIVE
  To investigate the effect of low O2 tension during in vitro culture in terms of ongoing pregnancy rates in ovum donation cycles.
  
  
  METHODS
  Randomized trial.
  
  
  METHODS
  Private university-affiliated IVF center, university-based hospital.
  
  
  METHODS
  A total of 1,125 cycles of ovum donation.
  
  
  METHODS
  Embryo culture in an atmosphere of 5.5% CO2, 6% O2, and 88.5% N2 versus a dual-gas system of 5.5% CO2 in air.
  
  
  METHODS
  Ongoing clinical pregnancy rates per intention-to-treat (ITT) patients.
  
  
  RESULTS
  The use of low O2 tension achieved a 41.3% ongoing pregnancy rate per ITT compared with a 40.8% rate obtained for 5% CO2 in air. The mean number of blastomeres and the percentage of top-quality embryos were significantly higher after lower O2 concentration during in vitro culture (7.1 ± 3.6 and 28.6% vs. 7.3 ± 8.4 and 32.1%, respectively).
  
  
  CONCLUSIONS
  In the ovum donation cycles undergoing day-3 embryo transfers, the use of low O2 tension did not improve ongoing pregnancy rates per cycle and per transfer. However, it benefited embryo quality, demonstrating the potential negative impact of high O2 tension on the in vitro embryo development.
authors.affiliation: Institut Universitari IVI, Valencia, Spain. mariajose.delossantos@ivi.es
authors.forename: Maria J
authors.initials: MJ
authors.lastname: de los Santos
authors.forename: Pilar
authors.initials: P
authors.lastname: Gámiz
authors.forename: Carmela
authors.initials: C
authors.lastname: Albert
authors.forename: Arancha
authors.initials: A
authors.lastname: Galán
authors.forename: Thamara
authors.initials: T
authors.lastname: Viloria
authors.forename: Sonia
authors.initials: S
authors.lastname: Pérez
authors.forename: Josep Ll
authors.initials: JL
authors.lastname: Romero
authors.forename: José
authors.initials: J
authors.lastname: Remohï
mesh_terms: D000328:Adult; D046149:Embryo Culture Techniques / Q000379:methods / Q000592:standards; D004624:Embryo Transfer / Q000706:statistics & numerical data; D004622:Embryo, Mammalian / Q000166:cytology* / Q000187:drug effects*; D005260:Female; D005307:Fertilization in Vitro / Q000706:statistics & numerical data; D006801:Humans; D008875:Middle Aged; D018587:Oocyte Donation / Q000379:methods / Q000706:statistics & numerical data*; D009994:Osmolar Concentration; D010100:Oxygen / Q000494:pharmacology*; D011247:Pregnancy; D018873:Pregnancy Rate; D011312:Pressure; D011786:Quality Control
chemical_list: D010100:Oxygen
keywords: Ovum donation; embryo quality; low oxygen tension; ongoing pregnancy rates