What is the primary effect of teratogenic agents?

Teratogenic agents are substances that can cause malformations or developmental abnormalities in embryos or fetuses during pregnancy. Their primary effect is to induce birth defects, which can range from structural abnormalities to functional impairments in the developing organism. These agents can disrupt normal cellular processes during critical periods of fetal development, leading to a wide array of issues such as physical deformities, organ malformations, and other developmental challenges.

The other options represent health effects that are not the specific concern of teratogenic agents. While triggering allergic reactions, causing respiratory problems, and leading to behavioral issues can be relevant to other types of toxic agents or insults, they do not encompass the core impact of teratogens, which specifically relates to congenital abnormalities and the overall integrity of fetal development. Thus, the identification of birth defects as the primary effect aligns accurately with the definition and understanding of teratogenic agents.