Teratogen

A teratogen is an agent or factor that can cause congenital abnormalities or fetal functional deficits when a fetus is exposed during pregnancy. Teratogens include certain medications, recreational or occupational chemicals, infectious agents, radiation, and maternal conditions such as diabetes or malnutrition. The risk and spectrum of effects depend on the dose, duration of exposure, the developmental stage of the fetus, and individual genetic susceptibility.

Critical periods of development influence susceptibility. The highest risk for structural anomalies occurs during organogenesis in the first trimester, especially between about weeks 3 and 8. Some exposures can also cause growth restriction, intellectual impairment, or later-onset disorders even if facial or limb malformations are not evident. Classic examples include alcohol leading to fetal alcohol spectrum disorders, isotretinoin causing craniofacial and cardiac defects, and thalidomide producing limb abnormalities. Infections such as rubella, cytomegalovirus, and Zika virus can also act teratogenically, as can radiation and some chemicals.

Assessment of teratogenic risk relies on animal studies, human observational data, and pharmacovigilance. Prevention emphasizes avoidance of known teratogens during pregnancy, vaccination against preventable infections, and nutritional measures such as folic acid supplementation to reduce neural tube defects. When exposure cannot be avoided, counseling and risk-reducing strategies are essential. Drug labeling and regulatory programs, including pregnancy-purity controls in certain medications, aim to minimize fetal risk and guide reproductive decision-making.

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