Does Endometrial Thickness Predict Chemical Pregnancy in Frozen Embryo Transfer? Analysis of 522 artificial cycles performed by a single physician.

Abstract

Objective: To evaluate whether endometrial thickness (EMT) is associated with pregnancy rates in frozen embryo transfer (FET) cycles.

Methods: This retrospective study analyzed medical records of patients who underwent FET between January 2021 and December 2024. All procedures were conducted by the same physician, using standardized endometrial preparation, with blastocyst-stage transfers. EMT was measured by transvaginal ultrasound on the day of transfer, and pregnancy was confirmed by β-hCG > 25 mIU/ml approximately two weeks later. Statistical analysis included Mann-Whitney U test, linear regression, ROC curve analysis, and chi-square tests, with significance defined as p≤0.05.

Results: A total of 522 FET cycles were performed, after exclusions, such as untreated uterine infertility factors and cryopreserved cleavage stage embryos, 478 patients were included with a chemical pregnancy rate of 70.29%. Participants' median age was 34.9 years (range 23-49). EMT ranged from 3.6 to 20mm (mean 8.82mm). ROC analysis identified 8.3 mm as the optimal cutoff (AUC=0.55; sensitivity 0.542; specificity 0.518). No significant differences were found in pregnancy rates between different EMT intervals (≤8.3mm vs. >8.3 mm, p=0.4944; <7 mm vs. ≥7mm, p=0.1036). Regression analysis showed no significant association between EMT and pregnancy (b=-1.205; p=0.3182; 95% CI: -3.914 to 1.504).

Conclusion: In our study, EMT did not significantly predict pregnancy outcomes in FET cycles, indicating that the cancellation of embryo transfers should not be canceled solely on the basis of endometrial thickness.