The in vitro fertilized oocytes continue to develop and form embryos. In the early stages of development, the embryos consist of well distinct cells, the blastomeres and are surrounded by a transparent membrane, the zona pellucid. By the end of the first day after the fertilization, the embryos are expected to have completed the first division and to have 2 cells, at the second day 4 cells and at the third day 8 cells. During the time embryos are kept in the laboratory, they are placed in appropriate culture media inside incubators to ensure the appropriate culture conditions. The embryologist observes the embryos daily and evaluates their morphology and development.