Fertilized egg with sperm in fallopian tube is carried to uterus, and then development starts. This video shows the early stages of human development. After fertilization, one of the earliest phase is to form blastocyste. Approximately 5 days later, inside the blastocyste, inner cell mass (ICM) is formed. Those cells make up the entire human. And the embryo plants into uterus and human grows on there until the birth.