Fetus

A fetus is the prenatal stage of a viviparous mammal between the embryonic stage and birth; in humans, this begins at the ninth week of gestation. In pharmacology, the fetus is not classified as a molecular target but is considered a highly sensitive patient population and a site for potential drug-induced toxicity or therapeutic intervention. Drugs reaching the fetus must typically cross the placental barrier, where they may interact with fetal-specific isoforms of enzymes or receptors. Understanding the physiological and developmental state of the fetus is essential for evaluating the safety profiles of maternal medications and for the field of fetal therapy, which aims to treat conditions like congenital diaphragmatic hernia or cardiac arrhythmias in utero.

Other names

Unborn offspringDeveloping embryo (post-organogenesis)

The fetus is a multicellular organism rather than a molecular target. Drugs interact with specific receptors, enzymes, or signaling pathways within fetal tissues or the placenta to exert therapeutic or toxic effects (e.g., corticosteroids inducing surfactant production via glucocorticoid receptors).