What is the definition of a teratogen?

A teratogen is defined as a substance that interferes with normal fetal development, leading to potential malformations or developmental anomalies in an embryo or fetus. This can include a variety of agents such as certain medications, alcohol, infectious agents, and environmental chemicals. The critical aspect of teratogens is their ability to disrupt the intricate processes of development during the early stages of pregnancy, which can result in serious birth defects or functional impairments.

In contrast, substances that aid in fetal nutrition do not pose a risk to development; they support it. Genetic disorders, while important in the context of fetal health, are not classified as teratogens. Similarly, vaccines given during pregnancy are designed to protect both the mother and fetus from disease, and while they can affect immune development, they are not considered teratogens unless specifically shown to cause harm, which is typically not the case with recommended vaccinations. Thus, the understanding of teratogens focuses on those agents that cause negative impacts on fetal development.