During which developmental phase is the impact of teratogens most significant?

The impact of teratogens is most significant during embryonic development. This is a critical period when the foundation for all major organ systems is established, typically occurring between the 3rd and 8th week of gestation. During this phase, the developing embryo is highly sensitive to external agents that can cause malformations or developmental issues, as the cells are rapidly dividing and differentiating into specialized tissue.

Exposure to teratogens during this period can disrupt normal growth and lead to congenital malformations, miscarriage, or severe developmental disorders. The developing structures are particularly vulnerable to the effects of teratogens because they are still in the process of forming; any interference can have lasting consequences.

In contrast, during conception, teratogenic effects are minimal as the zygote is still a single cell and not yet differentiated. Fetal development, which takes place after the embryonic phase, is marked by growth and maturation of already formed structures; while teratogens can still affect this phase, the potential for malformation is generally lower than in the embryonic phase. Neonatal care does not involve development in utero, so the direct impact of teratogens is no longer applicable at this stage.