During pregnancy, which stage is most directly harmed by teratogens?

The correct answer is that the embryo is the stage most directly harmed by teratogens. During the embryonic stage, which occurs from the third to the eighth week of pregnancy, the major organs and structures of the body are forming. This period is crucial because the developing embryo is particularly vulnerable to external agents, such as teratogens, which can disrupt the normal development of these critical systems.

Teratogens include substances like drugs, alcohol, certain infections, and environmental toxins, and exposure during this stage can result in significant developmental issues, including physical malformations and complications that could affect the health of the child.

In contrast, while the fetal stage, which occurs after the embryonic stage, can also be affected by teratogens, many core structures and systems have been laid down by this point. Though risks remain, particularly concerning growth and fine-tuning of development, the potential for severe malformative effects is generally greater during the embryonic stage. Neonates and infants are post-birth stages where while teratogenic effects may still be relevant, the most critical effects related to the formation of the body and organ systems have already occurred.