Final answer:
Teratogens are agents that can cause birth defects during fetal development. They include chemicals, drugs, and other substances that can harm the developing embryo or fetus, causing a range of physical and cognitive issues.
Step-by-step explanation:
​Substances that cause birth defects are best defined as Teratogens. These are environmental agents, including biological, chemical, or physical factors, that can harm the developing embryo or fetus. Some common examples of teratogens are alcohol, cigarette smoke, prescription drugs like warfarin and Accutane, as well as illegal drugs such as cocaine and heroin.
When a woman is exposed to teratogens during pregnancy, the risk of birth defects can increase significantly. The type and severity of defects may vary based on the potency of the teratogen, the duration of exposure, and the stage of fetal development during exposure. Teratogenic effects can include a wide range of physical and cognitive developmental issues, with some like fetal alcohol spectrum disorders having lifelong consequences.