FIGURE 3.

Schematic illustrating the multifunctional importance of STB for healthy pregnancy. A cross section of a chorionic villus near term is shown. O₂, micronutrients, immunoglobulins, water, and various other substances pass across the STB layer to gain access to blood vessels in the villus core, through which they can be carried to the fetus. CO₂ and waste products diffuse across the STB layer from fetal to maternal blood. STB also produces and secretes a variety of factors into maternal blood, including peptide and steroid hormones, growth factors, EVs, and larger vesicles (e.g., syncytial knots). Given the diverse functions of STB for pregnancy success and its contiguity with maternal blood, aberrant STB function can contribute to adverse pregnancy outcomes.