Teratogens are substances or factors that can cause malformation or developmental issues in a fetus during pregnancy. These can include certain medications, alcohol, drugs, infections, and environmental toxins. Exposure to teratogens can lead to a range of birth defects, affecting physical and cognitive development. The effects of teratogens depend on various factors, including the timing of exposure, the dose, and the genetic susceptibility of the fetus. For example, exposure to alcohol during pregnancy can lead to Fetal Alcohol Spectrum Disorders, while certain infections like rubella can cause serious complications. Understanding teratogens is crucial for promoting healthy pregnancies.