Front Matter

123 45678916 20–36

Period of dividing zygote, Embryonic period, weeks Fetal period, weeks

implantation and embryo,

weeks

Palate Ear Brain

Palate

Ear

Ear

Eye

Eyes

Eye

Eye

Heart

Heart

Upper limbs

Lower limbs

Not susceptible to teratogens

Prenatal death Major congenital anomalies (red)Functional defects and minor congenital anomalies

Central nervous system

Te eth

External genitalia

Heart

38

External genitalia

Figure 1.16 Developmental progression and susceptibility to teratogens and fetal loss.
The bars indicate periods when organs are most sensitive to damage from teratogenic
agents. Note that in most literature development of the olfactory system is missing.
The brain starts developing 18 days after fertilization. Often women do not know that they
are pregnant until after a few weeks have passed. Therefore, pregnant women who are
exposed to certain synthetic fragrances, either through inhalation or epidermal exposure,
and food‐flavor chemicals, through ingestion (e.g., teas, chewing gum, and other food
flavors), may put their embryo at risk without even knowing it. Source: Adapted from Ref. [8].