Two different concentrations of oxygen for culturing precompaction stage embryos on human embryo development competence: a prospective randomized sibling-oocyte study.

The study was to investigate the effects of oxygen concentration at different levels for culturing pre-compaction embryos on human embryo development competence. A total of 1254 oocytes from 92 patients treated with conventional in vitro fertilization (IVF) were harvested in this study. Oocytes were randomly assigned to the atmospheric (~20%) or low (~5%) oxygen concentration groups on the retrieval day (day 0). Groups were compared with respect to fertilization rates, embryo development, and reproductive outcome. We failed to detect a significant difference on fertilization rate between two groups. However, the low oxygen group yielded more optimal embryos on day 3 when compared with the atmospheric group (72.4% vs. 64.2%). The low oxygen group had a significantly higher blastocyst formation rate than the atmospheric oxygen group (64.5% vs. 52.9%). It is seemly that the optimal blastocyst and frozen blastocyst rates was higher in the low oxygen group, but the data did not reach a statistical significance. Although the use of low oxygen will not affect the clinical outcome in the fresh cleavage-transfer cycles, but it will result in more favorable clinical outcomes in the subsequent warming blastocyst-transfer cycles, with statistically significantly higher clinical pregnancy rate (CPR) and implantation rate (IR) compared with atmospheric oxygen. In conclusion, a low oxygen concentration may significantly improve the developmental potential of pre-compaction embryos, thus resulting in a positive effect on subsequent blastocyst cultivation and optimizing the treatment cycle.