Abstract Study question What significance does progesterone levels hold on the day prior to the transfer of euploid embryos, and how is this correlated with pregnancy rates? Summary answer Progesterone levels prior to embryo transfer play a crucial role in endometrial receptivity What is known already In the realm of assisted reproductive technology, creating optimal conditions for embryo transfer is crucial for successful pregnancies. Progesterone, a key hormone for endometrial receptivity, plays a pivotal role in this process. This retrospective observational study aims to evaluate the importance of progesterone levels the day before euploid embryo transfer and their correlation with pregnancy rates. For this reason, we study patients with low progesterone levels prior to transfer and the effectiveness of “rescue protocols”. Study design, size, duration This was a Retrospective Observational Study, that covers 121 women who underwent embryo transfer (euploid embryos and oocyte donation) who had their progesterone measured the day before the transfer, from January 1st 2023– December 31st 2023. The primary endpoint was pregnancy rate. Participants/materials, setting, methods During the study period, endometrial preparation was carried out by administration of progesterone, both orally or vaginally. The patients were divided into three groups based on the level of progesterone the day before the embryo transfer. • >10ng/mL • 8-10 ng/mL • <8ng/mL. These participants were treated with the daily administration of 1 or 2 doses of injectable Prolutex until confirmation of pregnancy by ultrasound. Eligible patients were aged ≤50 years with adequate endometrium thickness after receiving estrogen. Main results and the role of chance Preliminary findings underscore a significant correlation between progesterone levels exceeding 10 ng/ml the day before embryo transfer and elevated pregnancy rates. Conversely, in cases with lower progesterone levels, a personalized supplementation approach involving Prolutex demonstrates positive impacts on pregnancy outcomes. This highlights the pivotal role of tailored progesterone supplementation, utilizing Prolutex, in enhancing endometrial receptivity and, consequently, elevating the likelihood of successful pregnancies. The study emphasizes the need for personalized strategies, shedding light on the nuanced interplay between progesterone levels, supplementation methods, and the potential influence on reproductive success. As we explore these results, it becomes evident that chance alone does not govern outcomes; rather, strategic interventions hold the key to optimizing the path to successful pregnancies. Limitations, reasons for caution The main limitation of the study is the lack of randomized control studies. Furthermore, in this study, we are not including as the main group those who with low progesterone do not undergo rescue intervention with Prolutex. Wider implications of the findings Preliminary findings reveal a substantial link between progesterone levels exceeding 10 ng/ml before embryo transfer and heightened pregnancy rates. Conversely, in cases of lower progesterone, personalized Prolutex supplementation positively influences outcomes, emphasizing the pivotal role of tailored progesterone strategies in optimizing endometrial receptivity for successful pregnancies. Trial registration number not applicable