How can drugs interfere with fetal development?

Drugs can interfere with fetal development primarily by crossing the placental barrier, a process that allows many substances to reach the fetus. Substances that cause physical defects during this period are known as teratogens.123

The impact of these drugs depends heavily on the timing of exposure. The first trimester, particularly the period of organogenesis, is the most critical phase; exposure during this time can lead to structural malformations, growth restriction, or fetal death. Mechanisms of interference include direct cell death in the developing embryo or indirect harm caused by maternal toxicity, which may deprive the fetus of essential nutrients or oxygen.34

While some medications are essential, many others—including certain anesthetics, analgesics, sedatives, and antibiotics—can have adverse effects. Consequently, it is a fundamental ethical principle in medicine that the potential for fetal harm must be carefully considered whenever maternal drug therapy is contemplated. Women are generally advised to avoid all non-essential drugs during pregnancy. Furthermore, drugs can also affect development if they damage the genetic material of spermatozoa in males.12