ABSTRACT
Teratogens are chemicals or drugs that cause toxicity to an embryo by inducing structural malformations, physical dysfunction, behavioral alterations, or genetic abnormalities in the fetus. The expression of the teratogenic response-the embryotoxic effect of a compound on the growth and development of the fetus-is usually manifested at birth or in the immediate postnatal period. A chemical may also interfere with the reproduction by inducing toxicity early in the reproductive cycle (fi rst trimester) by impairing fertilization or by interfering with implantation. Thus, the initial interaction of a fertilized ovum and exposure to a suspected teratogen may result in the inability to establish pregnancy or induction of its spontaneous termination.
