What is an embryo?
As embryo (Greek embryo = unborn) living beings are referred to at a very early stage of development. How far reaches this stage of embryonic development, there is no agreement among scientists so far.
There are basically two views regarding the onset of the embryonic phase:
1.) With the fertilization of the egg.
2.) After cell differentiation with emergence of cotyledons (during gastrulation).
The European Court of Justice recently dealt with the question of what constitutes an embryo in the legal sense. Currently, it was about the patentability for the use of stem cells from unfertilized oocytes. In a previous ruling from 2011 it had been established that embryos were not used for the purpose of stem Cell research may be killed. The procedure should now highlight whether or not unfertilized oocytes are already considered embryos.
In the Opinion of the Advocate General of the ECJ, it was stated that an embryo is "every human egg from the stage of its fertilization". For the complete procedure, see here.
After application and training of the internal organs, for example between weeks 8 and 10 of pregnancy, the embryo is henceforth called the fetus.