Impact of oxygen tension according to embryo stage of development: a prospective randomized study

Abstract

Human embryo culture under 2–8% O2 is recommended by ESHRE revised guidelines for good practices in IVF labs. Nevertheless, notably due to the higher costs of embryo culture under hypoxia, some laboratories perform embryo culture under atmospheric O2 tension (around 20%). Furthermore, recent meta-analyses concluded with low evidence to a superiority of hypoxia on IVF/ICSI outcomes. Interestingly, a study on mice embryos suggested that oxidative stress (OS) might only have an adverse impact on embryos at cleavage stage. Hence, we aimed to demonstrate for the first time in human embryos that OS has a negative impact only at cleavage stage and that sequential culture conditions (5% O2 from Day 0 to Day 2/3, then «conventional» conditions at 20% O2 until blastocyst stage) might be a valuable option for human embryo culture. 773 IVF/ICSI cycles were included in this randomized clinical trial from January 2016 to April 2018. At Day 0 (D0), patients were randomized using a 1:2 allocation ratio between group A (20% O2; n = 265) and group B (5% O2; n = 508). Extended culture (EC) was performed when ≥ 5 Day 2-good-quality-embryos were available (n = 88 in group A (20% O2)). In subgroup B, 195 EC cycles were randomized again at Day 2 (using 1:1 ratio) into groups B’ (5% O2 until Day 6 (n = 101)) or C (switch to 20% O2 from Day 2 to Day 6 (n = 94). Fertilization rate, cleavage-stage quality Day 2-top-quality-embryo (D2-TQE), blastocyst quality (Day 5-top-quality-blastocyst (D5-TQB) and implantation rate (IR) were compared between groups A and B (= cleavage-stage analysis), or A(20% O2), B’(5% O2) and C(5%-to-20% O2). Overall, characteristics were similar between groups A and B. Significantly higher rates of early-cleaved embryos, top-quality and good-quality embryos on Day 2 were obtained in group B compared to group A (P < 0.05). This association between oxygen tension and embryo quality at D2 was confirmed using an adjusted model (P < 0.05). Regarding blastocyst quality, culture under 20% O2 from Day 0 to Day 6 (group A) resulted in significantly lower Day 5-TQB number and rates (P < 0.05) compared to both groups B’ and C. Furthermore, blastocyst quality was statistically equivalent between groups B’ and C (P = 0.45). At Day 6, TQB numbers and rates were also significantly higher in groups B’ and C compared to group A (P < 0.05). These results were confirmed analyzing adjusted mean differences for number of Day 5 and Day 6 top quality embryos obtained in group A when compared to those respectively in groups B’ and C (P < 0.05). No difference in clinical outcomes following blastocyst transfers was observed. These results would encourage to systematically culture embryos under hypoxia at least during early development stages, since OS might be detrimental exclusively before embryonic genome activation.

GRP78 acts as a cAMP/PKA signaling modulator through the MC4R pathway in porcine embryonic development

“…Previous studies have used blastocyst diameter and total cell number to assess blastocyst quality, 29,30 and oxidative stress is also an indicator of blastocyst quality 31,32 ; therefore, these parameters were examined to determine blastocyst quality. Studies have shown that blastocyst quality is critical for embryonic stem cell production and other related applications 33,34 .…”

Oxidative Stress and Assisted Reproduction: A Comprehensive Review of Its Pathophysiological Role and Strategies for Optimizing Embryo Culture Environment

“…More recent studies indicated that low oxygen levels (5%) during embryo culture favor increased the number of mitochondria in blastomeres in mice [83], and blastocyst development and pregnancy rates [84][85][86] in humans as compared to culture in higher (20%) oxygen concentration. Embryos are particularly sensitive to OS induced by high (20%) atmospheric oxygen concentration at the early stages before embryonic genome activation [87]. ROS levels in media cultured under 5% oxygen were found to be lower than that under atmospheric oxygen concentrations [87].…”

“…Embryos are particularly sensitive to OS induced by high (20%) atmospheric oxygen concentration at the early stages before embryonic genome activation [87]. ROS levels in media cultured under 5% oxygen were found to be lower than that under atmospheric oxygen concentrations [87].…”

Maternal exposure to hyperbaric oxygen at the preimplantation stages increases apoptosis and ectopic Cdx2 expression and decreases Oct4 expression in mouse blastocysts via Nrf2‐Notch1 upregulation and Nf2 downregulation

“…[1][2][3] Subtle changes of the environmental oxygen tension during preimplantation development both in vivo and in vitro have been reported to significantly alter the rates of cleavage, implantation and pregnancy, the quality and cell numbers of cleaved embryos and blastocysts, global expression of genes and proteins in blastocysts, and optimal pluripotency gene expression during embryogenesis of bovine, murine, and human embryos. [1][2][3][4][5] While the in vitro hypoxic culturing at 5% oxygen (O 2 ) has been shown to be beneficial for increasing both the developmental rate and cell numbers in both the ICM and whole human and murine embryos via upregulated expression of the pluripotency genes and proteins including POU5F1 (OCT4), SOX2 and NANOG, and cell proliferation by hypoxia inducible factors, 1,3 longer in vitro culture under an extremely lower oxygen tension, namely 2% O 2 , is detrimental for mouse preimplantation embryogenesis, at least in part attributable to a significantly decreased level of histone lactylation. 5 On the other hand, parental exposure to varied oxygen tensions may impact the quality and imprinted gene expression of gametes and hence further disrupt embryonic development after fertilization.…”

“…It has been well‐documented that the physiological oxygen tensions between 1.5 and 8.7% within the female reproductive tract are optimal for mammalian embryonic development and pluripotency gene expression 1–3 . Subtle changes of the environmental oxygen tension during preimplantation development both in vivo and in vitro have been reported to significantly alter the rates of cleavage, implantation and pregnancy, the quality and cell numbers of cleaved embryos and blastocysts, global expression of genes and proteins in blastocysts, and optimal pluripotency gene expression during embryogenesis of bovine, murine, and human embryos 1–5 .…”