Compacted Thin Endometrium and Reproductive Outcomes in Frozen Embryo Transfer
Abstract
Background: Endometrial thickness (EMT) is a key predictor of success in frozen-thawed embryo transfer (FET), but a 'thin' endometrium often poses clinical dilemmas regarding cycle progression. Recent evidence suggests that endometrial compaction—a decrease in EMT after progesterone
exposure—may reflect physiological receptivity rather than pathological thinning. However, its prognostic value in patients with thin EMT on transfer day is not yet established.
Objectives: To assess the impact of endometrial compaction on live birth rates (LBR) in women with thin EMT (<8 mm) on the day of FET.
Materials and Methods: This retrospective study analyzed 85 artificial FET cycles (2018–2020) with EMT <8 mm on transfer day. Cycles were categorized into two groups based on endometrial compaction, defined as a ≥5% decrease in EMT between the end of the estrogen phase and transfer day.
Results: The compaction (n=53) and non-compaction (n=32) groups had comparable EMT on transfer day (7.65 vs. 7.79 mm; p = 0.162). However, the compaction group demonstrated significantly higher clinical pregnancy rates (47.2% vs. 21.9%; p = 0.023) and live birth rates (37.7% vs. 15.6%; p = 0.048) compared to the non-compaction group.
Conclusion: A thin endometrium on transfer day is not universally associated with poor prognosis. If the "thin" phenotype results from physiological compaction rather than insufficient proliferation, pregnancy outcomes remain favorable. Distinguishing between compacted and intrinsically thin endometria is critical to avoid unnecessary cycle cancellations.
Keywords
endometrium, frozen embryo transfer, pregnancy outcome, live birth, ultrasonography
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