Does culture of embryos in an ultra-low (2%) oxygen environment yield better blastocyst development than 6% oxygen using time-lapse morphokinetics?

Abstract

Objective To evaluate if culture of mouse embryos in an ultra-low oxygen environment could enhance blastocyst development in terms of time-lapse morphokinetics. Design Prospective study Materials and methods A total of 214 commercially obtained frozen mouse embryos (B6D2F1 & B6C3F1 hybrid) were thawed and cultured in One-Step medium with 10%SPS using an EmbryoScope time lapse incubator at 37°C, 5.5% CO2, and either (1) 6.0% O2 (n=106) or (2) 2.0% O2 (n=108) Embryo images were recorded every 10 minutes for 6 days of culture. Time lapse videos were annotated for the following time points: 2cell (t2), 3cell (t3), 4cell (t4), 5cell (t5), 6cell (t6), 7cell (t7), 8cell (t8), start of compaction (tSC), morula (tsM), start of blastulation (tSB), blastocyst (tB), expanded blastocyst (tEB) and hatching blastocyst (tHB). The 2-cell stage was considered as time zero since the exact time of insemination was unknown. Time points were statistically compared between the two groups. Blastocyst development rates for both culture environments were also compared. Results There were no statistically significant differences between the two groups in any of the time points measured up to the 8-cell stage. However, after the 8-cell stage, the 2% O2 group showed significantly slower embryo development for each time point up to the hatching blastocyst stage. There was no difference in the blastocyst development rate between the 6% O2 and 2% O2 environments (99.1% vs 95.4%). Conclusions Our data did not show any benefit of culturing embryos in a 2% oxygen environment. Although there was no difference in the blastocyst development rate between culturing in 2% and 6% oxygen, the 2% oxygen group took significantly longer to reach the blastocyst stage than the 6% oxygen group. Disclosures Nothing to disclose Funding None