Received September 09, 2021
Accepted May 30, 2023

Objective: The use of frozen embryos in the treatment of infertility with assisted reproductive techniques has been increased. Different methods are used to prepare the endometrium for frozen embryo transfer (FET). The aim of this study was to compare the pregnancy outcomes after treatment with tamoxifen and Hormonal replacement therapy (HRT) in FET. Methods: This randomized clinical trial study was carried out on 214 infertile women in the infertility research center of Milad Hospital in Mashhad during 2018-2020. 84 patients received tamoxifen and 93 of them took HRT. Endometrial thickness (ET) and pregnancy outcome were measured in both groups. Results: Mean duration of infertility (P = 0.328), number of embryos (P = 0.649), FSH (P = 0.390) and LH / FSH ratio (P = 0.287) as well as type of infertility (primary and secondary) (P = 0.307), causes of infertility (P = 0.703) and pattern of menstruation (P = 0.306) were not significant difference in two groups. But the mean LH of patients in the TMX group was significantly higher than the HRT group (P = 0.051). Mean ET in the TMX and HRT were 8.90 ± 0.88 mm and 8.99 ± 0.85 mm, respectively (p = 0.57). There was no statistically significant difference between chemical pregnancy (P =0.705), clinical pregnancy (P =0.688) and ongoing pregnancy (P =0.923) in TMX and HRT groups. Conclusion: treatment with Tamoxifen can be as effective as GnRH agonist for endometrial preparation in FET. Keyword: Tamoxifen, IVF, GnRH agonist, Frozen embryos transfer, endometrial thickness