1. A method of determining the well being of a placenta in a pregnant woman having a maternal-placenta-fetal system, the method comprising the steps of: (a) simultaneously monitoring selected maternal and fetal physiological signals; (b) using said physiological signals for identifying a mathemaical model describing the maternal-placenta-fetal system, and mathematical parameters describing said model; and (c) determining, according to said mathematical model and said mathematical parameters describing said mathematical model, the well being of the placenta.