[Cytotrophoblastic invasion is the most important mechanism of placentation and pregnancy progression].

The paper presents new Russian and foreign materials on cytotrophoblastic invasion, the most important mechanism of interaction between the placenta, fetus, and mother during the progression of physiological pregnancy. The original classification of placental cell development has been published; the initial wave of invasion, the main and additional ways of its implementation in the second trimester, and the formation of cytotrophoblastic plugs in the spiral arteries, and the fate of multinucleated giant cells have been characterized. Additional sources of invasive cells in the second trimester are presented. A general concept of cytotrophoblastic invasion as a regulator and main mechanism of transition from the histotrophic to more effective hemochorial type of fetal nutrition has been made. The modern definition of an invasive process is given. This information is important for obstetricians and pathologists who analyze the causes of obstetric complications.