Background: Frozen embryo transfer has become one of the main therapeutic approaches for infertility. Endometrial preparation is a key process in endometrium receptivity and treatment outcomes; there are two primary approaches for endometrial preparation, i.e., natural cycle and hormone replacement therapy (HRT). In the current study, we investigated modified natural cycle (MNC) with HRT in terms of endometrial thickness, biochemical pregnancy, clinical pregnancy, and ongoing pregnancy rates