Hoechst and TUNEL staining of blastocyst inner cell mass (ICM). Frequency histogram of ICM with different number of apoptotic cells evaluated by the nuclear staining, Hoechst 33342, of the embryo outgrowth cultured in control or composite-conditioned medium (C-CM) in three independent experiments. B) Pictures of representative ICM and trophoblast outgrowth cultured in control (upper) or composite-conditioned medium (below) stained with Hoechst 33342 (left) and by TUNEL method (right). The arrows indicate TUNEL-positive apoptotic cells. Note several TUNEL-positive cells in the ICM of a blastocyst cultured in C-CM. Magnification approximately 100×. All parameters were evaluated by observation under a phase contrast microscope as reported in the tests and showed in Figures 1, 2, 3. The results were obtained in at least three different experiments.