RESUMO
OBJECTIVE: To compare the effect of two oxygen concentrations used during days 3-5 of human embryo culture on embryo quality and pregnancy outcome. DESIGN: Retrospective analysis of the use of two culture conditions. SETTING: University-based infertility clinic. PATIENT(S): Three hundred eighty-two patients undergoing IVF. INTERVENTION(S): 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. MAIN OUTCOME MEASURE(S): Embryo quality, pregnancy rates, and implantation rates. RESULT(S): 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%). CONCLUSION(S): 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.