Teratogens are

• A. Chemicals that can cause developmental malformations to unborn fetuses
• B. Infectious diseases
• C. Genetic mutations
• D. Drugs that have no effect on development

Answer: (A)

Teratogens are agents that can cause developmental malformations in a fetus when exposure occurs during pregnancy. This definition fits best with the idea that chemicals can disrupt fetal development and lead to birth defects, which is why this option is the most accurate among the choices. Timing and dose matter: exposure at certain stages of development can produce specific defects, while other exposures might have little or no effect. While some infections can be teratogenic and genetic mutations can cause congenital issues, teratogens are external agents that interfere with development, not inherited changes. A drug that has no effect on development would not be a teratogen.