Background. Refractory pregnancy loss (RPL) is a multifactoral pathology in women of reproductive age which treatment represents great difficulties. Great role in RPL pathogenesis is stipulated by chronic endometritis resulting from disturbances of implantation followed by gestational sac malfunction, which is not less significant than progesterone deficiency. Objective. The aim of research was to study the dynamics of ultrastructural changes of endometric epithelial cells in the conditions of pre-conception preparation in refractory pregnancy loss. Methods. 63 samples of endometrium bioptates obtained from female patients of reproductive age with insufficient middle luteal phase of the cycle were studied. Light and electronic microscopy was used to study the morphological changes in endometric epithelial cells. Results. Pre-conceptional cyclic hormone therapy (1 mg 17-estradiol and 20 mg of didrogesteron) in comparison with monotherapy of 20 mg of didrogesteron during 3 months contributed to intracellular regeneration and restoration of secretor phenotype of endometrium epithelial cells corresponding to the status of receptivity with “opened window of implantation”. Conclusions. Cyclic hormonotherapy in combination with complex metabolic therapy as a pre-conceptional preparation contributing to pregnancy illustrates much higher effectiveness of pathogenetically proved preconceptional hormonotherapy KEY WORDS: refractory pregnancy loss, endometrium receptivity, hormone therapy, ultrastructure.