The early embryo primarily depends on mitochondria for energy production. We have previously shown that metabolite levels differ in slow and fast embryos. Our goal therefore is to observe mitochondrial function in early embryos. Slow growing embryos stained with TMRM (mitochondrial membrane potential) and CM-H2DCFDA (ROS) displayed higher fluorescence than fast growing embryos. This indicates that slow embryos may be associated with overcompensation in the OXPHOS pathway, which subsequently produces high levels of ROS. We used qPCR to determine the expression of GLYCOX (GAPDH, HK) and OXPHOS (ATP5b, COX5a) genes. Slow 8-cell embryos expressed higher levels of ATP5b and both slow morula and blastocyst embryos had high expression of GAPDH. Treatment with CoQ10 improved cleavage rate. In the presence of CoQ10, fast 8-cell embryos expressed lower GAPDH and slow 8-cell embryos expressed higher ATP5b. These results show a possible over compensation of slow embryos in response to impaired mitochondrial function.