R Taheripanah - Infertility and Reproductive Health Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran

Endometrium is one of the most important factors in assisted reproductive technology cycles. Thin endometrium with frequency of 2.4% in assisted reproductive technology cycles is associated with lower implantation and pregnancy rate. The appropriate endometrium is 7-10 mm for embryo transfer. Inflammatory, iatrogenic and idiopathic causes lead to thin endometrium .Thin endometrium is characterized by poor growth of glandular epithelium, high uterine blood impedance and low VEGF that causes of poor vascular development and further decrease of blood flow. Chronic endometritis with destroy of the estrogen receptors has a crucial role in refractory endometrium to hormonal preparing. Different modalities were explained to improve the endometrial growth and higher thickness such as intrauterine injection of G-CSF, extended higher dose of estragon support , adding the low dose hCG during the hormonal preparing for frozen embryo transfer. Other modalities such as intrauterine autologous platelet rich plasma infusion, luteal phase support with GnRH agonist was reported but none of them have been substantiated. Recently, intrauterine administration of bone marrow stem cell, progenitor cells was reported from the IVI center but their efficacy is unknown. Also, Sildenafil, tocopherol, aspirin, and Larginine, pentoxifylline have been used to improve endometrial vascularity in unresponsive endometrium. In addition to lower implantation, the process of invasion may be hindered due to the lack of an adequate endometrial bed and increases the placenta accrete rate. Bone marrow mesenchymal stem cells (BMSCs) improved endometrium thickness, probably via their migration and immunomodulatory. The best protocol for embryo transfer in thin endometrium cases is the FET due to better endometrial thickness without fair of the embryo destroys.