Background:Assisted reproductive technologies (ART) rely heavily on optimizing endometrial preparation for successful Frozen-Thawed Embryo Transfer (FET). Progesterone plays a crucial role in modulating endometrial receptivity, yet its specific influence in FET outcomes remains intricate and multifaceted.Methods:This study investigates the impact of progesterone and estrogen treatment on ongoing pregnancy rates in FET cycles. A standardized hormonal protocol involving exogenous estradiol (E2) and progesterone was employed. Endometrial thickness and compaction were meticulously assessed throughout the cycle.Result:The Clinical Pregnancy Rate (CPR) in the Compaction group stands at 57.6%, whereas the Increased ET group exhibits a lower CPR of 36.4%. Remarkably, the No compaction group shows the lowest CPR at 6% (p = 0.039). Further breakdowns depict distinct trends in pregnancy outcomes. Live birth rates are notably higher in the Compaction group (100%) compared to the Increased ET and No compaction groups (0%) (p = 0.042). Although no significant differences are observed in the Abortion rates across groups (p = 0.155), the Compaction group displays the highest rate at 57.1%. Ectopic pregnancies, prevalent in both Compaction and Increased ET groups (50% each), are absent in the No compaction group (p = 0.245).Conclusion:Progesterone's influence on endometrial dynamics is multifaceted, shaped by individualized responses. Individualized approaches, considering both quantitative and qualitative aspects of compaction, are essential for optimizing FET success.