RESUMEN
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 pregnancy outcomes after treatment with tamoxifen and hormonal replacement therapy (HRT) in FET. METHODS: This randomized clinical trial was carried out with 214 infertile women in the infertility research center of Milad Hospital in Mashhad during 2018-2020. We had 84 patients receiving tamoxifen and 92 took HRT. Endometrial thickness (ET) and pregnancy outcome were measured in both groups. RESULTS: Mean infertility duration (p=0.328), number of embryos (p=0.649), FSH (p=0.390), LH (p=0.051) and LH/FSH ratio (p=0.287) as well as type of infertility (primary or secondary) (p=0.295), causes of infertility (p=0.750) and pattern of menstruation (p=0.676) were not significantly different in the two groups. Mean ET in the TMX and HRT groups were 8.72±1.45mm and 9.00±1.69mm, respectively (p=0.423). There was no statistically significant difference between chemical pregnancy (p=0.663), clinical pregnancy (p=0.994) and ongoing pregnancy (p≥0.999) in the TMX and HRT groups. CONCLUSIONS: Treatment with tamoxifen can be as effective as GnRH agonist for endometrial preparation in FET.