![]() Indeed, two studies found that the biphasic strategy led to an increase in the total blastocyst rate 12 and the usable blastocyst rate 16. Few studies reported a significant increase of the blastocyst rates in culture with biphasic (5–2%) O 2 compared with monophasic (5%) O 2 concentration 12, 16, but these results remain controversial 10. Hence, implementing a biphasic (5–2%) O 2 concentration strategy in IVF laboratories seems relevant, especially because of the increasing use of extended culture up to the blastocyst stage 15. In humans, O 2 concentration is approximately 5% in the fallopian tube from the fertilization stage to the cleaved embryo stage, and approximately 2% in the uterus from the morula to the blastocyst stage 8, 13, 14. Interestingly, recent data suggest that dynamic O 2 exposure during in vitro culture might represent a more physiological environment, thus potentially improving IVF outcomes 8– 12. Therefore, a continuous level of 5% O 2 is currently used in most IVF laboratories for preimplantation human embryo culture 7. However, a recent meta-analysis confirmed the significant increase in live birth rate when using monophasic 5% O 2 compared with monophasic 20% O 2 5. requirement of a nitrogen gas system, specialized incubators, and additional quality assurance associated with oxygen sensors) 2, 5, 6. In the last 40 years, the majority of IVF laboratories worldwide used atmospheric (≈ 20%) O 2 concentration for preimplantation embryo culture, mainly to limit the additional costs associated with the use of low O 2 concentrations (e.g. Many studies provided evidence about the key role of oxygen (O 2) concentration during preimplantation embryo development 2. ![]() ![]() temperature, pH, culture medium composition) 1, 3, including the gas composition inside the incubator during in vitro embryo culture 1, 2, 4. ![]() This “back to nature” approach concerns different parameters (e.g. One approach to increase IVF outcomes is to improve the in vitro microenvironment by mimicking the in vivo conditions, to promote embryo development and increase the implantation potential 1, 2. The biphasic (5–2%) O 2 concentration strategy for preimplantation embryo culture could increase the “take home baby rate”, thus improving IVF cost-effectiveness and infertility management.ĭuring in vitro fertilization (IVF), many exogenous factors can affect human embryo development, such as light, temperature, and chemical compounds 1. These genes are mainly involved in embryo development, DNA repair, embryonic stem cell pluripotency, and implantation potential. Whole transcriptome analysis of blastocysts donated for research identified 707 RNAs that were differentially expressed in function of the O 2 strategy (fold-change > 2, p value < 0.05). 44.1%, p = 0.027) were significantly higher with the biphasic (5%-2%) O 2 concentration strategy. 32.8%, p = 0.002, respectively) and the cumulative live birth rate (17.9% vs. The total and usable blastocyst rates (44.4% vs. Embryos were cultured at 5% from day 0 (D0) to D5/6 (monophasic O 2 concentration strategy) in the first IVF cycle, and at 5% O 2 from D0 to D3 and 2% O 2 from D3 to D5/6 (biphasic O 2 concentration strategy) in the second IVF cycle. This hypothesis was tested in this monocentric observational retrospective study that included 120 couples who underwent two IVF cycles between 20. A “back to nature” approach could increase in vitro fertilization (IVF) outcomes. Oxygen (O 2) concentration is approximately 5% in the fallopian tube and 2% in the uterus in humans.
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