Endometrial compaction is associated with the increased live birth rate in artificial frozen-thawed embryo transfer cycles

We aimed to assess the effect of endometrial compaction on the live birth rate in frozen-thawed embryo transfer (FET) cycles and to investigate the parameters associated with compaction. FET cycles performed in a tertiary care infertility centre between May 2013 and October 2019 were reviewed retrospectively. The decremental change of endometrial thickness between the end of oestrogen phase and ET day was defined as endometrial compaction. The primary outcome measure was endometrial compaction, and the secondary outcome was the live birth rate. Among all, 89 had endometrial compaction and 194 did not. The live birth rate was significantly higher in the compaction group (23.6 vs. 13.4%, respectively; p = 0.039). Multivariate logistic regression analysis revealed that in FET cycles with artificial endometrial preparation, the chance for live birth was significantly higher in cycles with endometrial compaction [OR: 3.133, 95% confidence interval (CI) 1.104-8.892; p = 0.032] when adjusted for age, stage of the embryo, and endometrial thickness at the end of the oestrogen phase. According to receiver operating characteristic (ROC) curve analysis the sensitivity and specificity of 9.25 mm endometrial thickness at the end of oestrogen phase were 76.4 and 58.8%, respectively (area under the curve: 0.701, 95% CI 0.640-0.763; p < 0.001) to predict endometrial compaction.