The state of pregnancy is very complex and interesting because of many adaptations that transpire in the mother's body. The mother's immune system must be tolerant of the partially allogeneic fetus and thus allow it to grow and develop without rejection, while at the same time protecting the mother and fetus from infection by pathogenic microorganisms. Changes in the maternal immune system occur in many areas during different stages of pregnancy. Hormone levels change during the various stages of pregnancy to allow implantation first, then fetal growth, and after development, affect the initiation of labour. At the same time, they affect the adaptations of other subgroups of the immune system. Deficient or incorrect adaptation of organ systems to pregnancy leads to serious complications in pregnancy, such as preeclampsia, recurrent miscarriages, or premature birth, which can, in the worst case, lead to the death of the mother or fetus. The diploma examines changes in the level of NK cells, macrophages, B and T cells, cytokines and chemokines, adjustments of the hormonal system in pregnancy and its impact on other organ systems, and the severity and susceptibility to infections during pregnancy.