A teratogen is anything that can disrupt the healthy development of a baby during pregnancy. When a pregnant person is exposed, it can increase the risk of birth defects, growth problems, developmental delays, or long-term health issues.

How serious the effects are depends on several factors — including when during pregnancy the exposure happens, how much of the teratogen is present, and the baby’s genetic vulnerability.

Teratogens are generally grouped into five categories. For clarity, we have separated medications from chemicals, since chemicals are more often encountered as environmental exposures.

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