What periods in the development of the embryo are called critical. Justify the need for knowledge of the features of these periods.

Critical periods of the individual development of the embryo are those stages that are characterized by increased sensitivity of the organism or its parts to the action of adverse environmental and internal factors, which can lead to structural abnormalities, congenital diseases, impaired growth and differentiation, and death of the embryo. During critical periods, the regulatory capabilities of a developing organism decrease, and this reduces its resistance to negative influences. Knowledge of critical periods in the development of the fetus is important for the development of methods for the protection of pregnancy and the corresponding periods of childhood.