Introduction: Loaded obstetric history (abortion, ectopic pregnancy, births), transfusions, hemoteraphy, grafts are risk factors for isoimmunization in Rh system. Patients and method: A special case of Rh isoimmunization is the girls having Rh negative from mothers with Rh positive, which can be izoimunizate without any obstetrical or transfusion history; isoimmunization occurs by transfer of maternal red blood cells Rh positive in the circulation of the Rh negative fetus; in terms of pregnancy with Rh positive fetus, amnestic reactions occur with significant increases in anti Rh antibody titer - theory "grandmother troublesome". Results: Rh negative pregnant woman with Rh -positive homozygous husband will certainly have Rh positive fetus. If the mother and fetus have ABO incompatibility, red blood cells Rh positive are destroyed by its group of agglutinins and Rh antigenic sites are masked for maternal immune system. Conclusions: Rh iso-immunization once installed can't be influenced downward by antibody titer, it is having irreversible changes.