Teratogens are more likely to cause damage during the embryonic stage and damage during the fetal stage.

Teratogens are more likely to cause the least damage during the embryonic stage and the most damage during the fetal stage. The embryo is most susceptible to teratogenic agents during periods of rapid differentiation. The stage of development of the embryo determines suscep-tibility to teratogens. The most critical period in the development of an embryo or in the growth of a particular organ is during the time of most rapid cell division.