Medications are essential in modern medical treatment. However, their use during pregnancy requires special caution because some drugs may affect fetal development. One important concept in pharmacology is chirality, which refers to the existence of molecules in two mirror-image forms. Although these forms have the same chemical formula, they may produce different biological effects. This paper discusses the concept of chiral drugs and their potential impact on the fetus during pregnancy. Chirality in Pharmacology Chirality is a chemical property in which a molecule exists as two non-superimposable mirror images called enantiomers. These enantiomers may interact differently with biological receptors in the body. In some cases, one enantiomer produces the desired therapeutic effect, while the other may be less effective or even harmful. Because of this, understanding chirality is very important in drug development and safety evaluation. Chiral Drugs During Pregnancy During pregnancy, many medications can cross the placenta and reach the fetus. Since the fetus is still developing, exposure to certain drugs may cause congenital malformations, growth problems, or developmental disorders. The risk becomes more complex with chiral drugs because each enantiomer may behave differently in terms of absorption, metabolism, and biological activity. One enantiomer may be relatively safe, while the other may have toxic or teratogenic effects. Historical Example: Thalidomide Thalidomide is one of the most well-known examples of drug-related fetal harm. In the late 1950s, it was prescribed to pregnant women to treat nausea and insomnia. Later, it was discovered that the drug caused severe limb deformities in thousands of newborns. This tragedy led to major changes in drug testing and regulation worldwide and emphasized the importance of studying stereochemistry in pharmacology. Mechanisms of Fetal Effects Chiral drugs may affect the fetus through several mechanisms: Differences in receptor binding affinity. Variations in maternal metabolism of each enantiomer. Differences in placental transfer. These factors can lead to different biological outcomes between the two mirror-image forms of the same drug. Preventive Measures To reduce fetal risk, healthcare professionals should: Carefully evaluate the safety of each enantiomer. Avoid unnecessary medication use during pregnancy. Prescribe drugs only when clearly needed. Prefer single-enantiomer formulations when available. Conclusion Chirality plays a significant role in pharmacology, especially in the context of pregnancy. Even small differences in molecular structure can result in major differences in biological activity and safety. Therefore, careful drug evaluation and responsible prescribing practices are essential to protect both maternal and fetal health. Al-Mustaqbal University is ranked first among Iraqi private universities.