After fertilization an embryo develops from the egg cell. By the second day after the egg cell removal it is already composed of 2 to 6 cells. The subsequent hours and days of development are decisive for the success of the treatment. There are continuous improvements made regarding the embryo culture. Incubators are constantly being improved in order to provide the perfect surroundings for the embryo, meaning a close replica of the conditions found in the body of the woman. The culture medium, in which the embryos are situated, is also continously enhanced.
Nevertheless, embryos from different couples vary and occasionally even embryos from the same couple and treatment cycle differ greatly from each other.