During the first week of pregnancy zygote is formed which then undergoes a series of mitotic division that gives rise to a 16 cell stage called morula.Morula on further division forms blastocyst and its implantation in the uterus occurs.
During the second week , this blastocyst fully gets implanted in the uterus and forms embryo.Now from the 3rd week onwards the development of embryo begins.Initially , the central nervous system is formed then during the next few weeks the heart , eyes and limbs take place , till 9th week the brain is formed that continues to grow till 16th week.
Then during proceeding months , the movement of the baby is observed , and its body is covered with fine hairs , eyelids also appear at this time.By the end of the embryonic stage , all essential external and internal structures have been formed.It is then reffered to as fetus.