The optimal method to prepare endometrium before frozen embryo transfer (FET) is not yet established. We retrospectively studied 4496 FET and detailed pregnancy and miscarriage rates in three groups of patients according to the endometrium preparation they have followed before their successive FET: clomifene citrate (CC, group 1), artificial cycle (AC, group 2) or switch between CC and AC (group 3). The overall pregnancy rates per transfer were 24.3, 20.8 and 17.3% while the miscarriage rates reached 23.2, 29.8 and 42.5%, respectively. Group 1 experienced the highest ongoing pregnancy rate (18.6%), the lowest being observed in group 3 (10.0%, p < 0.001). Here we propose several alternatives to improve our AC protocol (group 2) that seemed less effective than CC (group 1) and we consider the use of a gonadotrophin-stimulated treatment for patients with the lowest reproductive outcomes (group 3).
Keywords: Assisted reproductive technology; clomiphene citrate introduction; endometrium; frozen embryo transfer; hormone replacement therapy.