Clinical Value of Histologic Endometrial Dating in Women With Thin Endometrial Lining During Frozen-Thawed Blastocyst-Stage Embryo Transfer: A Retrospective Case Series

INTRODUCTION: To evaluate the pregnancy outcome of frozen embryo transfer (FET) cycles from patients with inadequate endometrium (IE) but “in-phase” histologic endometrial dating. METHODS: This is a retrospective pilot study of patients between the years of 2014 and 2020 who underwent a standard hormonal endometrial preparation for FET that had been canceled due to IE defined as a maximum thickness <8 mm following up to 35 days of estradiol supplementation. Endometrial biopsy was performed for histologic dating using the criteria of Noyes et al after 9–11 days of progesterone supplementation. Women who were determined to have “in-phase” endometrium underwent a subsequent FET cycle in the following month, utilizing the same endometrial proliferation method and transferred of at least one good-quality blastocyst. The EMT goal was determined from the previous cycle. The primary outcome was the live birth rate. Descriptive statistics and Pearson Correlation was calculated using SPSS software v23. RESULTS: A total of 21 women were included. The mean age was 38.2±6.7 years. The mean endometrial thickness was 6.4±0.5 mm. Seventeen women (81%) demonstrated endometria that were “in-phase” on histological dating and underwent a subsequent FET cycle: The mean number of embryos transferred was 1.47±0.6, the live birth rate was 35.3% (6/17); clinical pregnancy rate was 47% (8/17); miscarriage rate was 11.8%. There was no correlation between age and endometrial thickness (Pearson Correlation Coefficient R=0.08, P =.7). CONCLUSION: Histologic dating in women with a prior canceled FET due to IE is a potentially reliable method to allow the opportunity for a successful FET with comparable outcomes to the National Average (SART National Summary Report for 2018).