title: Low versus atmospheric oxygen tension for embryo culture in assisted reproduction: a systematic review and meta-analysis.
abstract: To appraise the available evidence comparing low oxygen (LowO2) and atmospheric oxygen tension (AtmO2) for embryo culture.
  
  
  
  Systematic review and meta-analysis.
  
  
  
  Not applicable.
  
  
  
  Women undergoing assisted reproduction using embryo culture.
  
  
  
  Embryo culture using LowO2 versus AtmO2.
  
  
  
  Reproductive, laboratory, and pregnancy outcomes.
  
  
  
  A total of 21 studies were included in this review. All used O2 concentration between 5% and 6% in the LowO2 group. Considering the studies that randomized women/couples, we observed very low quality evidence that LowO2 is better for live birth/ongoing pregnancy (relative risk [RR] = 1.1, 95% confidence interval [CI] 1.0-1.3) and clinical pregnancy (RR = 1.1, 95% CI 1.0-1.2). Considering the studies that randomized oocytes/embryos, we observed low quality evidence of no difference of fertilization (RR = 1.0, 95% CI 1.0-1.0) and cleavage rate (RR = 1.0, 95% CI 1.0-1.1), and low quality evidence that LowO2 is better for high/top morphology at the cleavage stage (RR = 1.2, 95% CI 1.1-1.3). No studies comparing pregnancy outcomes were identified. Several studies used different incubators in the groups-a new model for the LowO2 group and an old model for the AtmO2 group. The risk of detection bias for the laboratory outcomes was high as embryologists were not blinded.
  
  
  
  Although we observed a small improvement (∼5%) in live birth/ongoing pregnancy and clinical pregnancy rates (PRs), the evidence is of very low quality and the best interpretation is that we are still very uncertain about differences in this comparison. The clinical equipoise remains and more large well-conducted randomized controlled trials are needed. They should use the same incubators in both groups and the embryologists should be blinded at least when evaluating laboratory outcomes.
authors.affiliation: Department of Obstetrics and Gynecology, Ribeirao Preto Medical School, University of São Paulo, Ribeirao Preto, Brazil.
authors.forename: Carolina O
authors.initials: CO
authors.lastname: Nastri
authors.affiliation: Department of Obstetrics and Gynecology, Ribeirao Preto Medical School, University of São Paulo, Ribeirao Preto, Brazil.
authors.forename: Beatrice N
authors.initials: BN
authors.lastname: Nóbrega
authors.affiliation: Department of Obstetrics and Gynecology, Ribeirao Preto Medical School, University of São Paulo, Ribeirao Preto, Brazil.
authors.forename: Danielle M
authors.initials: DM
authors.lastname: Teixeira
authors.affiliation: Department of Obstetrics and Gynecology, Ribeirao Preto Medical School, University of São Paulo, Ribeirao Preto, Brazil.
authors.forename: Jowanka
authors.initials: J
authors.lastname: Amorim
authors.affiliation: Department of Obstetrics and Gynecology, Ribeirao Preto Medical School, University of São Paulo, Ribeirao Preto, Brazil.
authors.forename: Lívia M M
authors.initials: LMM
authors.lastname: Diniz
authors.affiliation: Department of Obstetrics and Gynecology, Ribeirao Preto Medical School, University of São Paulo, Ribeirao Preto, Brazil.
authors.forename: Marina W P
authors.initials: MWP
authors.lastname: Barbosa
authors.affiliation: Department of Obstetrics and Gynecology, Ribeirao Preto Medical School, University of São Paulo, Ribeirao Preto, Brazil.
authors.forename: Vanessa S I
authors.initials: VSI
authors.lastname: Giorgi
authors.affiliation: Department of Obstetrics and Gynecology, Ribeirao Preto Medical School, University of São Paulo, Ribeirao Preto, Brazil.
authors.forename: Vicky N
authors.initials: VN
authors.lastname: Pileggi
authors.affiliation: Department of Obstetrics and Gynecology, Ribeirao Preto Medical School, University of São Paulo, Ribeirao Preto, Brazil. Electronic address: wpmartins@gmail.com.
authors.forename: Wellington P
authors.initials: WP
authors.lastname: Martins
mesh_terms: D001274:Atmospheric Pressure; D001755:Blastocyst / Q000378:metabolism*; D046149:Embryo Culture Techniques; D010064:Embryo Implantation; D005260:Female; D005307:Fertilization in Vitro / Q000009:adverse effects; D006801:Humans; D050498:Live Birth; D016017:Odds Ratio; D010100:Oxygen / Q000378:metabolism*; D011247:Pregnancy; D018570:Risk Assessment; D012307:Risk Factors; D016896:Treatment Outcome
chemical_list: D010100:Oxygen
keywords: Embryo culture; ICSI; IVF; assisted reproductive techniques; meta-analysis; oxygen