When a teratogenic drug is taken during pregnancy, the fetal effects are typically observed in:

The fetal effects of teratogenic drugs are typically observed in certain target organs in a predictable manner due to the biological mechanisms underlying teratogenesis. Teratogens are substances that can cause developmental abnormalities in a fetus during specific periods of pregnancy, often during organogenesis when critical structures are forming.

Each teratogen has a specific action and tends to affect particular stages of development and specific target organs. For instance, some drugs may primarily impact the development of the heart, while others may affect the central nervous system, limbs, or facial structures. The predictable nature of these effects is backed by extensive research and understanding of developmental biology and pharmacology, which provide insight into how and when certain drugs can disrupt normal development processes.

Also, the timing of exposure to teratogens is crucial. For example, exposure during critical periods of organ development often leads to consistent defects, whereas exposure outside of these critical windows may not result in observable effects. This predictability highlights the importance of avoiding known teratogenic substances during pregnancy and informs healthcare providers about the potential risks associated with specific medications.