Fig. 1. Strategy for synchronizing pre-implantation embryos at compaction and the timing of morphogenetic events during the analyzed period. Embryos were selected at the onset of compaction (about 60 to 70 hp-hCG; 0 hp-compaction). Groups of embryos were fixed every 5 hours, through morula and blastocyst stages bI to III, until 55 hp-compaction, corresponding to embryonic days (E) 2.5 to 4.5.