A high incidence of permanent embryo arrest occurs during the first week of in vitro development. We hypothesize that this developmental arrest event is regulated by the stress adaptor protein p66^shc, a genetic determinant of life span in mammals, which regulates ROS metabolism, apoptosis, and cellular senescence. The aim of this study was to assess the relationship between intracellular oxidative stress levels with the incidence of embryo arrest and the expression of senescent-associated genes in embryos produced under different oxygen tensions. Embryos cultured under 20% oxygen conditions showed approximately 10-fold increase in oxidative stress, 2-fold increase in the percentage of 2- to 4-cell arrest, and significantly lower developmental capabilities compared to embryos cultured under a 5% oxygen environment. Quantification by real-time PCR and by semiquantitative immunofluorescence showed significantly higher p66^shc mRNA and protein levels, respectively, in embryos cultured in 20% versus those cultured in 5% oxygen atmosphere. No significant changes in p53 mRNA and protein levels were detected among embryos derived from both oxygen tensions. Taken together, these results demonstrate that p66^shc, but not p53, is significantly more abundant in an embryo population that exhibits higher frequencies of embryo arrest and quantities of intracellular ROS. These results further substantiate that p66^shc and oxidative stress are associated with a p53-independent embryonic arrest event for in vitro-produced embryos.