Effect of ultra-low O2 (2%) tension on human in-vitro embryo development

The study was aimed to investigate the effect of culturing human in-vitro embryos in ultra-low O₂ (2%) tension. A total of 2298 oocytes from 152 patients between June 2017 and December 2017 treated with conventional in vitro fertilization (IVF) were harvested in this study. Oocytes were randomly assigned to the low (5%) or ultra-low (2%) O₂ tension groups on the retrieval day. We observed that the day 3 good quality embryos (43.32 versus 42.01%; p=.635) and available embryos (82.02 versus 83.47%; p=.490) rates were similar between 2% and 5% condition. No differences were observed in the D5 blastulation rate (62.79 versus 61.85%; p=.735) and the proportion of good quality blastocysts on Day 5 (44.51 versus 45.61%; p=.700), nor in the total blastulation rate (71.26 versus 70.29%; p=.710) between 2% and 5% condition. In the first transfer, the blastocysts had similar clinical pregnancy (68.12 versus 71.08%; p= .692) and ongoing pregnancy (59.42 versus 62.65%; p=.684) rates from 2% and 5% condition. The employ of ultra-low O₂ tension did not benefit for human in-vitro embryo development.