The placental barrier is a critical physiological structure in mammalian pregnancy, serving as the interface between the maternal and fetal circulations. This barrier is essential for the exchange of nutrients, gases, and waste products while protecting the developing fetus from harmful substances and pathogens. The placental barrier is selectively permeable and comprises several layers, including the trophoblast cell layer, basement membranes, and fetal endothelial cells. However, not all toxic substances are completely blocked, making maternal exposure to toxins and infections a concern for fetal development. The efficiency and selectivity of the placental barrier are crucial for fetal development and a successful pregnancy outcome.