Representative confocal images illustrating apoptosis frequency in six–eight-cell mouse embryos subjected to TUNEL analysis. Positive control embryo nuclei in the blue (A) and green (B) fluorescence channels, and (C) merged image. Embryo nuclei in the blue (D) and green (E) fluorescence channels, and (F) merged image. (G) Apoptosis rates of fresh and thawed embryos in the normal-weight and obese groups. Apoptosis rate = TUNEL + blastomeres/total number of blastomeres. Each group contained 40–50 embryos. The apoptosis rate was significantly higher in fresh embryos in the obese (vs. normal-weight) group, but did not differ between groups of thawed embryos.