Have we neglected the role of fetal endothelium in transplacental transport?

Maternal-to-fetal transfer of nutrient and other substances occurs across the placental barrier (PB) which is made up of endothelial cells (EC) on the fetal side and the syncytiotrophoblast (STB) on the maternal side. Numerous studies were conducted to explore the transport characteristics across the STB layer, which is also considered as the major resistance for maternal-to-fetal exchange of materials. In contrast the layer of EC has received very little attention if at all. A recently developed viable co-culture model of the PB revealed significant resistance of the EC layer for maternal-to-fetal transfer of glucose. This argues for a major contribution of the EC to overall transplacental transfer of nutrients. Accordingly, it is recommended to fill the void of knowledge and expand our understanding on the role of the feto-placental endothelium for transplacental transport characteristics.