embryological development /-loj″ik/ , the various intrauterine stages and processes involved in the growth and differentiation of the conceptus from the time of fertilization of the ovum until the eighth week of gestation. The stages are related to the biological status of the unborn child and involve the differentiation of the various cells, tissues, and organ systems and the development of the main external features of the embryo. It occurs from approximately the end of the second week to the eighth week of intrauterine life. The fetal stage follows these stages, beginning at about the ninth week of gestation. The entire process of growth and development of the embryo and fetus is loosely called prenatal development. See also prenatal development.
