Influence of human embryo cultivation in a classic CO₂ incubator with 20% oxygen versus benchtop incubator with 5% oxygen on live births: the randomized prospective trial

Abstract

SummaryOur objective was to assess the effect of benchtop incubators with low oxygen concentrations on the clinical and embryological parameters of our patients. We conducted a prospective, randomized, opened controlled trial on infertile patients in stimulated cycles. In total, 738 infertile patients were assessed for eligibility and, after final exclusions, 230 patients were allocated either to a 5% O2 group (benchtop incubator) or a 20% O2 group (classic incubator). Finally, 198 patients in the 5% O2 group and 195 in the 20% O2 group were analysed. The outcomes measured were fertilization rate, clinical pregnancy rate, and live birth rate. The primary outcome – live birth rate per all transfers – did not show any improvement in the 5% oxygen group over the 20% oxygen group (25.3% versus 22.6%, P=0.531), but the number of day 5 blastocysts was significantly higher (P=0.009). Fertilization rate did not show any beneficial effect of reduced oxygen (5%) (73.4%±22.4% versus 74.6%±24.0%, P=0.606) per all transfers but there was statistically significant difference in the day 5 SET subgroup (85.3±15.1 versus 75.1±17.5; P=0.004). Clinical pregnancy rate showed results in favour of the 5% oxygen group for all subgroups (day 3: 23.7% versus 21.1%, P=0.701; day 5 SET: 35.0% versus 30.6%. P=0.569) but showed statistical significance only in the day 5 SET subgroup (51.1% versus 29.8%; P=0.038). Culturing of embryos in benchtop incubators under low oxygen produced more blastocysts and therefore was a better alternative for embryo selection, which resulted in higher pregnancy rates. To achieve higher live birth rates, embryo quality is not the only factor.

Pre-Implantation Mouse Embryos Cultured In Vitro under Different Oxygen Concentrations Show Altered Ultrastructures

“…We decided to focus our analysis on embryos cultured with the same medium but different oxygen concentrations because reduced O 2 tension has resulted in improved development to the blastocyst stage [14]. The use of a low O 2 concentration is beneficial for embryo development in vitro to the blastocyst stage in mice [12,19,30,31], hamsters [32], rabbits [33], pigs [34], sheep [35] and humans [16,36].…”

“…Many studies in several species have demonstrated that pre-implantation embryo development is improved by culturing embryos under a lower concentration of O 2 [10][11][12], most likely because the physiological concentration of O 2 in vitro corresponds to the O 2 tension existent in the female reproductive tract [13,14]. Mammalian embryos cultured under a lower O 2 tension (5%) showed higher cleavage, implantation, pregnancy and live birth rates [15,16]. However, how different oxygen tensions affect the morphology of pre-implantation mouse embryos cultured in vitro is not completely understood.…”

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

“…Indeed, some of the studies evaluating the impact of oxygen on embryo development either describe the use of different kind of incubators (e.g. large-box incubators in atmospheric conditions and benchtop incubators in hypoxia) 15 , 20 , 28 , or do not specify the type of incubators used 4 . Large-box incubators are less stable than benchtop incubators, causing additional stress to embryos because of temperature and pH variations, and possibly affecting the conclusions of such studies.…”

Redox Regulation and Oxidative Stress in Mammalian Oocytes and Embryos Developed In Vivo and In Vitro

“…Given that 21% (atmospheric) O 2 results in increased ROS, many IVF clinics have switched to low-O 2 incubators to more closely mimic O 2 concentrations of 2-8% in the reproductive tract [63,65]. Several clinical trials have been carried out to determine the impact of low concentrations of O 2 on various parameters of fertility [226][227][228]. Culture of embryos in 5% O 2 increases the percentage developing to the blastocyst stage and their quality.…”

“…Culture of embryos in 5% O 2 increases the percentage developing to the blastocyst stage and their quality. However, there is limited evidence to show low O 2 improves live-birth rate [226][227][228]. Table 2.…”