Immunologic response modulation during pregnancy

Immunologic system is able to recognize the own and the non-own, therefore the curious question: Why the fetus is not rejected? Nowadays, it is known that during pregnancy there are physiological modifications about the innate immunity as in the adaptive one allowing fetus to develop without any aggression by the immune response of the mother against the environment aggressors. These changes manifesting in the immunologic system are consequences of hormonal variations associated with pregnancy due to the immunologic system cells and the release of cytokines is different in each trimester of pregnancy, now it is possible to know that the involvement of these cytokines is essential in the implantation of fetus, as well as in pathological processes associated with pregnancy including the pre-eclampsia and the spontaneous abortions.