A teratogen is any agent — a drug, infection, chemical, or radiation — that can disrupt prenatal development. But timing matters as much as the substance: the same teratogen can be devastating one week and nearly harmless the next. Drag a teratogen onto the timeline to find its window of greatest harm.
Prenatal timeline
Drag a teratogen onto the timeline—
Germinal (wk 1–2): all-or-none — exposure either ends the pregnancy or has little effect. Embryonic (3–8): organs are forming — greatest risk of major structural defects. Fetal (9–birth): growth and fine-tuning. Dark bars mark each organ's most sensitive weeks; weeks are counted from conception.