When is the fetus at the greatest risk for drug or medication interaction?

The fetus is at the greatest risk for drug or medication interactions during the first trimester. This period is critical for the development of the major organ systems, as it encompasses the first 12 weeks of pregnancy, when the foundations of vital structures are laid down. During this time, the fetus is particularly vulnerable to teratogenic effects from substances, meaning that exposure to certain drugs or medications can lead to significant developmental issues, birth defects, and other adverse outcomes.

This heightened sensitivity is due to the rapid cell division and differentiation occurring in the early stages of fetal development. The first trimester is when organs such as the heart, brain, and spinal cord are forming, making exposure to harmful substances particularly damaging. Additionally, the blood-brain barrier is not fully developed, which may enhance the risks associated with toxins or medications crossing into the fetal circulation.

In contrast, while the second and third trimesters are important for growth and development, the foundational structures have already been established by that point, leading to a lower risk of teratogenic effects. At birth, while certain medications may still affect the newborn, the critical developmental windows have passed, reducing the risk associated with earlier exposures. Therefore, understanding the timing of drug exposure relative to fetal development is crucial in prenatal