Because the majority of cell differentiation occurs during the phase, this is the time when exposure to teratogens can do the most damage.

Because the majority of cell differentiation occurs during the EMBRYONIC phase, The embryonic stage of pregnancy is the period after implantation during which all the important organs and structures in the growing fetus is formed. Tetratogens are factors that caused malformation of embryo. Exposure to tetratogens during embryonic stage cause most destructive damages.

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