The dynamics of the living human embryo is not well understood becouse of ethical and technical problems. We utilize human induced pluripotent stem (iPS) cells to avoid those problems, becouse the cells are derived from somatic cells, easily regulated, and correspond to epiblasts that give rise to fuman body. The overall goal of our research is to improve understanding of the flexibility and stability of stem cell-based systems for testing drug safety for unborn infants.