Background and Aim: Applying Assisted Reproductive Technologies (ARTs) is increasing. A critical step in ART is the frozen embryo transfer, in which the endometrium thickness has great significance in the outcome. In this case, the frozen embryo will be transferred during the next cycle. There are several ways to prepare an endometrium for transmitting embryos; however, choosing the best method remains debated. The present study aimed to evaluate the pregnancy rate of frozen embryo transfer in the presence or absence of GnRH agonists.
Methods & Materials: A retrospective analysis was conducted on 146 consecutive patients attending Qom’s infertility treatment center from 2015 to 2017; these subjects were candidates for the transfer cycle of the frozen-thawed embryo and randomly assigned to receive either protocol with or without GnRH agonist. Clinical features, implantation rate, pregnancy rate (chemical & clinical), and abortion rate were assessed.
Ethical Considerations: This study was approved by the Research Ethics Committee of the Academic Center for Education, Culture, and Research of Mashhad University (Code: IR.ACECR.JDM.REC.1398.001).
Results: There was no significant difference in baseline and clinical characteristics, implantation rate, pregnancy rate (chemical & clinical), and abortion rate between the study groups of endometrial preparations with or without GnRH agonist (P<0.05). 
Conclusion: In this study, pregnancy outcome was similar in both study groups; thus, this method is recommended as an endometrial preparation without GnRH agonist.