Which is NOT considered a teratogen?

A teratogen is any agent that can disturb the development of an embryo or fetus, leading to potential birth defects or abnormalities. In considering the options provided, birth control pills are designed primarily to prevent pregnancy by inhibiting ovulation and do not have a direct effect on fetal development when taken during pregnancy, as their primary function is to prevent conception in the first place.

Unlike environmental toxins, sexually transmitted infections (STIs), and certain drugs like diet pills, which can have harmful effects on fetal development if exposure occurs during pregnancy, birth control pills do not pose this risk in the same way. Their mechanism of action is to prevent rather than facilitate pregnancy, reducing the opportunity for any teratogenic effects to occur on a developing fetus. Consequently, they are categorized differently and are not regarded as teratogens.