In the placenta, maternal blood comes in direct contact with:
The syncytiotrophoblast forms the surface layer of the chorionic villi and is bathed by maternal blood flowing through the intervillous space. The syncytiotrophoblast is a product of division infusion of cells in the underlying cytotrophoblast. Fetal capillaries course through the fetal connective tissue that forms the core of all orders of villi, and thus have no contact with maternal blood when placental structure is intact. As the syncytiotrophoblast is a derivative of the embryonic trophoblast layer, it is incorrect to state that maternal blood has no contact with fetally derived cells. Ref: Cunningham F.G., Leveno K.J., Bloom S.L., Hauth J.C., Rouse D.J., Spong C.Y. (2010). Chapter 3. Implantation, Embryogenesis, and Placental Development. In F.G. Cunningham, K.J. Leveno, S.L. Bloom, J.C. Hauth, D.J. Rouse, C.Y. Spong (Eds), Williams Obstetrics, 23e.
The syncytiotrophoblast
The cytotrophoblast
Endothelial cells of fetal capillaries
Connective tissue cells of secondary villi