The transition from embryo to fetus
The transfer of an embryo into a fetus is not a biological process, but rather a matter of pure definition. It does not take place abruptly, but over the course of the past weeks. All organs are now formed and can partially fulfill their functions.
In addition, it is now clear that it is a developing human being. The weeks of development that now follow are characterized by the specialization of the cells and the growth in size of the individual organs. Only through this can an organism as complex as the human being develop.
A major difference to embryonic development is the extent of head growth. If this is strongly disproportionate in the first weeks, the speed slows down and other areas of the body are the focus of growth. Thus the body now grows mainly in length.
Only starting from the 5th month the weight follows this rapid course. The viability of the fetus outside the uterus, as a result of premature birth, is currently (2017) the 23rd week of pregnancy and a birth weight of at least 500g.
