In the fourth week the embryo has the aspect and size of a bean. It already has the three main tissue layers from which the rest of organs will be produced.
By Paloma de la Fuente Vaquero M.D., Ph.D., M.Sc. (gynecologist), Zaira Salvador B.Sc., M.Sc. (embryologist) and Marie Tusseau (invitra staff).
Last Update: 11/05/2018