Initially, an embryo grows as a single cell and then divides after every 12-24 hours. By Day 3, it is about 4-8 cells and it is known as a multicell embryo. All of the energy and chemicals, which are required for cell division, come from the mother’s egg at the time of early growth of the multicell embryo. By Day 5, the embryo is also referred as a blastocyst, is about 70-100 cells. A blastocyst contains inner cell mass and trophoblast. Approximately one third of embryos can successfully activate their genes and grow to the blastocyst stage.