Impact of Endometrial Compaction on Pregnancy Outcomes in Hormone Replacement Treatment–Frozen Embryo Transfer Cycles: A Prospective Cohort Study

evaluation of the endometrium is the most extensively utilized method, attributed to its noninvasive nature, cost-effectiveness, and widespread availability. 4This assessment typically includes the evaluation of endometrial thickness (EMT), volume, echogenic pattern, vascularity, and contractility.Of these parameters, EMT is the most frequently assessed, although its ability to reliably IntroductIonOver recent decades, the escalating burden of infertility has driven significant advancements in, and widespread adoption of, assisted reproductive technology (ART).Despite these advancements, the live birth rates (LBR) remain the primary constraint in achieving the overall success of ART.The "freeze-all" strategy represents a significant advancement in ART, involving the vitrification of all embryos for transfer in a future cycle.This approach presents several advantages, including a reduced risk of ovarian hyperstimulation syndrome (OHSS), enhanced endometrial receptivity, and improved embryo-endometrium synchronization, thereby becoming increasingly favored in clinical practice. 1he success of frozen embryo transfer (FET) relies not only on its primary factors-embryo and endometrial receptivity-but also on the synchronization between them. 2 The "window of implantation" (WOI) is the term used to describe the transient phase of endometrial receptivity that occurs during the mid-luteal phase.Although its precise timing, duration, and molecular basis remain unclear, it is generally thought to last 2-4 days.3 Disruptions or alterations in the WOI have been linked to infertility, recurrent implantation failure (RIF), pregnancy loss, and potentially preeclampsia.2 Various markers, encompassing both invasive and noninvasive approaches, have been proposed for the assessment of endometrial receptivity.