The study of human placental development has proven difficult, largely due to the inability of researchers to derive self-renewing trophoblast stem cells that retain the full differentiative potential of native placental trophoblast. Current studies are mostly done through mouse models or the culture of primary trophoblast cells. These methods of studying placental development are not ideal for understanding human placental development due to the differences between humans and mice and the limited proliferative and differentiative potential of available human primary trophoblast cells.