Advantages of Early Intrauterine Transfer of "Blank" Culture Medium Prior to 1st or 2nd Transfer of Thawed Embryo(s). Randomized, Single-blind, Multicenter Controlled Trial.

Despite technical advances in Medically Assisted Reproduction (AMP), the success of fertility treatments is sometimes limited by embryo implantation failure. The coordinated development of the embryo and the uterine endometrium requires close communication between the maternal tissue and the embryo. In in vitro fertilization (IVF), embryo transfer generally takes place between the 2nd (D2) and the 6th (D6) day following oocyte fertilization. Recent studies have shown the advantages of sequential transfer (transfer of an embryo on D2/D3 followed by the transfer of another embryo on D5/D6), with higher implantation and clinical pregnancy rate, fewer miscarriages, more live births, and yet no increase in multiple pregnancies. However, the American Society for Reproductive Medicine recommendations continue to prioritize the transfer of a single embryo for all patients aged under 38. To improve pregnancy rates for patients having a single embryo transferred, the study investigators wish to carry out on "blank" transfer, based on the principle of sequential transfer. The study investigators hypothesize that a culture medium, placed in the uterus before the time of embryo transfer, will modify immune tolerance. The study will test whether transferring the same culture medium in an equivalent quantity as during the real transfer into the uterus 2/3 days before the embryo transfer will improve tolerance to this foreign medium and, therefore, embryo implantation. The aim of this study is thus to evaluate the impact of a "blank" transfer with culture medium alone, on the results of frozen embryo transfers (FET) from IVF.