Objective. To investigate the features of the clinical course of experimental demyelinating pathology as a model of multiple sclerosis in rats in different trimesters of pregnancy. Material and methods. We used 48 nonlinear white female rats to study an effect of pregnancy on susceptibility to and clinical features of demyelinating pathology. Results and сonclusion. Severity of disease was shown to be a priority risk factor of pregnancy, which is realized depending on the period of gestation. An increase of representation and aggravation of the reproductive pathology during modeling of multiple sclerosis in II trimester indicates a risk of relapse in the late periods of reproduction cycle, derogates the idea about total retentive influence of pregnancy on the development of demyelinating events.