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 ...