Impact of Tamoxifen on Endometrial Thickness in Women With Thin Endometrium Following Estrogen Therapy During Frozen–Thawed Embryo Transfer

Endometrial thickness (ET) is an important parameter of determining endometrial receptivity for in vitro fertilization (IVF) with frozen-thawed embryo transfer (FET). ET is influenced by various intrinsic and extrinsic factors, such as hormonal fluctuations, age-related changes, underlying medical conditions, and metabolic factors. However, there are few published studies examining the effect of tamoxifen on endometrial development during IVF. The aim of this study was to evaluate the impact of tamoxifen on endometrial growth in patients undergoing IVF-FET who experienced a thin endometrium during their previous transfer cycle while undergoing estrogen therapy. This pilot study was conducted at Hazrate Zeinab Hospital, affiliated to Shiraz University of Medical Sciences in Shiraz, Iran, between 2019 and 2021. The study involved three infertile females aged 31-40 years who were referred to our center for IVF-FET. We recorded the patients' demographic and medical characteristics, the type of infertility, and the cause and duration of infertility. ET was measured using ultrasonography before the treatment began. Patients were then administered tamoxifen at a dosage of 20 mg per day, starting on the second day of their menstrual cycle for a duration of 5 days. On the seventh day of menstruation, a follow-up transvaginal ultrasonography was performed to assess the ET and evaluate the trilinear pattern. In our study of three patients with a history of inadequate response to high-dose estrogen, the endometrium improved in two patients and thickened by up to 7 mm, indicating a positive effect of tamoxifen on improving endometrial thickness.