Centre for Reproductive Medicine, Universitair Ziekenhuis Brussel, Laarbeeklaan 101, Brussels, Belgium.
Hum Reprod. 2019 Feb 1;34(2):228-234. doi: 10.1093/humrep/dey370.
Is a reduction in the oxygen tension from 5 to 2% during extended culture from Day 3 onwards beneficial for human blastocyst development in vitro?
A reduction in oxygen concentration from 5 to 2% O2 after Day 3 did not improve embryo development, quality and utilization rate.
The human embryo leaves the fallopian tube to reach the uterine cavity around Day 3-4 post-ovulation. As the oxygen concentration ranges from 5 to 7% in the fallopian tube and decreases to 2% in the uterus, reducing the oxygen tension during extended culture from Day 3 onwards seems more physiological. We aim to mimic the in-vivo environment during in-vitro embryo culture. Therefore, we compared the effect of extended culture performed at 5% (control arm) or 2% oxygen (O2; study arm) tension on blastocyst formation and quality.
STUDY DESIGN, SIZE, DURATION: Between December 2016 and September 2017, in two prospective studies, sibling embryos were randomized on Day 3 to either 5% O2 (control) or 2% O2 (study) for extended culture. In the control arms of both studies 1 and 2, the dishes with blastocyst medium were pre-equilibrated overnight in 5% O2, 6% CO2 and 89% N2 at 37°C. In the 2% study groups, the overnight pre-equilibration of blastocyst media was performed in either 2% O2 (study 1, 99 cycles) or 5% O2 (study 2, 126 cycles). The latter provides a gradual transition from 5 to 2% O2 environment for the study arm.
PARTICIPANTS/MATERIALS, SETTINGS, METHODS: Embryo culture until Day 3 was always performed in 5% O2; if at least four embryos of moderate to excellent quality were obtained on Day 3, the sibling embryos were randomized to either 5% O2 or 2% O2 for extended culture. The endpoints were embryo development and quality on Day 5/6 and the utilization rate (embryos transferred and cryopreserved). Statistical analysis was performed using the chi-square test, a P-value of <0.05 was considered significantly different.
In study 1, 811 embryos were randomized on Day 3: 405 to the 2% O2 and 406 to the 5% O2 condition. No differences were observed in the blastulation rate (68.6 versus 71.9%; P = 0.319) and the proportion of good quality blastocysts on Day 5 (55.8 versus 55.2%; P = 0.888), nor in the utilization rate (53.1 versus 53.2%; P = 1.000). In study 2, 1144 embryos were randomized: 572 in each arm. Similarly, no significant difference was demonstrated in terms of the blastulation rate (63.6 versus 64.7%; P = 0.758), the proportion of good quality blastocysts (46.9 versus 48.8%; P = 0.554) or the utilization rate (49.8 versus 48.1%; P = 0.953).
LIMITATIONS, REASON FOR CAUTION: This study evaluated embryo development only until Day 5/6. The effect of oxidative stress on the developing embryo may only become evident at later stages (i.e. during implantation) and should therefore be studied in an RCT. The question also remains as to whether the switch to ultra-low oxygen tension from Day 4 onwards, when the embryo arrives in the uterus in vivo, would be preferential.
Based on the present study results, there is no benefit in lowering the oxygen tension from 5 to 2% from Day 3 onwards during extended human embryo culture.
STUDY FUNDING/COMPETING INTEREST(S): No funding was received for this study and the authors have no conflicts of interest to declare.
N/A.
在第 3 天之后的延长培养过程中，将氧气张力从 5%降低至 2%是否有利于体外人类囊胚的发育？
在第 3 天之后，将氧气浓度从 5%降低至 2%并没有改善胚胎的发育、质量和利用率。
人类胚胎在排卵后第 3-4 天离开输卵管进入子宫腔。由于输卵管中的氧气浓度在 5%至 7%之间，并且在子宫中降低至 2%，因此在第 3 天之后的延长培养过程中降低氧气张力似乎更符合生理条件。我们旨在模拟胚胎体外培养过程中的体内环境。因此，我们比较了在 5%氧气（对照臂）或 2%氧气（研究臂）张力下进行延长培养对囊胚形成和质量的影响。
研究设计、规模、持续时间：在 2016 年 12 月至 2017 年 9 月期间，在两项前瞻性研究中，将第 3 天的同卵胚胎随机分配到 5%氧气（对照）或 2%氧气（研究）进行延长培养。在两项研究的对照臂中，在第 3 天，将含有囊胚培养基的培养皿在 37°C 下预平衡过夜，氧气浓度为 5%、6%二氧化碳和 89%氮气。在研究臂的 2%组中，过夜预平衡囊胚培养基在 2%氧气（研究 1，99 个周期）或 5%氧气（研究 2，126 个周期）中进行。后者为研究臂提供了从 5%氧气环境向 2%氧气环境的逐渐过渡。
参与者/材料、设置、方法：胚胎培养直到第 3 天一直在 5%氧气中进行；如果在第 3 天获得至少 4 个质量中等至良好的胚胎，则将同卵胚胎随机分配到 5%氧气或 2%氧气进行延长培养。研究终点是第 5/6 天的胚胎发育和质量，以及利用率（移植和冷冻的胚胎）。使用卡方检验进行统计分析，P 值<0.05 被认为具有显著差异。
在研究 1 中，811 个胚胎在第 3 天被随机分配：405 个胚胎分到 2%氧气组，406 个胚胎分到 5%氧气组。在囊胚形成率（68.6%与 71.9%；P=0.319）和第 5 天的优质囊胚比例（55.8%与 55.2%；P=0.888），以及利用率（53.1%与 53.2%；P=1.000）方面，没有观察到差异。在研究 2 中，1144 个胚胎被随机分配：每个臂 572 个胚胎。同样，在囊胚形成率（63.6%与 64.7%；P=0.758）、优质囊胚比例（46.9%与 48.8%；P=0.554）或利用率（49.8%与 48.1%；P=0.953）方面，也没有显著差异。
局限性、谨慎原因：本研究仅评估了胚胎发育至第 5/6 天。氧化应激对发育中胚胎的影响可能仅在后期（即植入期）才变得明显，因此应在 RCT 中进行研究。此外，从第 4 天开始将氧气张力从 5%降低至超低水平是否更有利，这一问题仍有待探讨。
根据本研究结果，在延长人类胚胎培养过程中，从第 3 天开始将氧气张力从 5%降低至 2%并没有益处。
研究资金/利益冲突：本研究没有收到资金支持，作者没有利益冲突需要声明。
无。
