ABSTRACT
Drugs or chemicals that induce structural malformations, physical dysfunction, behavioral alterations, or genetic deÞciencies in the fetus, or impair fertility, are referred to as teratogens. The expression of the teratogenic response — i.e., 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. In addition, reproductive toxicity of a chemical may interfere early on in the reproductive cycle (Þrst trimester), by impairing fertilization or interfering with implantation. These initial interactions between the fertilized ovum and the chemical in question may result in the inability to establish pregnancy or may cause spontaneous termination of pregnancy.
