ABSTRACT
Atmospheric oxygen (approximately 20%) in culture significantly impairs preimplantation embryo development. However, it is not known whether all stages of preimplantation embryo development are susceptible to oxygen toxicity. This study investigated the temporal responses of preimplantation embryos to oxygen conditions in vitro. Mouse embryos were cultured in atmospheric (approximately 20%) or lower (5%) oxygen concentrations for the first 48 h, followed by culture in the same or reciprocal oxygen concentrations for another 48 h: group 1 (control, 5 and 5%); group 2 (5 and 20%); group 3 (20 and 5%); and group 4 (20 and 20%). Time-lapse microscopy was performed with imaging of individual embryos at 15-min intervals. Compared with embryos cultured in 5% oxygen, embryos cultured in 20% oxygen were delayed at the 1st cleavage by 0.45 h (P<0.05), at the 2nd cleavage by 0.84 h (P<0.01) and at the 3rd cleavage by 3.19 h (P<0.001). Switching from 20% to 5% oxygen after 48 h did not completely alleviate earlier induced perturbations. Partial or complete culture in atmospheric oxygen resulted in significantly fewer blastocyst cell numbers compared with control (P<0.05). Oxygen can influence mouse embryo development at both the cleavage and post-compaction stages.