B-cell lymphoma 6 expression significantly differs by the uterine preparation method used for frozen embryo transfer

OBJECTIVE: To determine whether B-cell lymphoma 6 (BCL6), an endometriosis-associated marker postulated to predict poor pregnancy outcomes, is differentially expressed in the window of implantation with various uterine preparation regimens commonly used for frozen embryo transfers. DESIGN: A retrospective cohort study. SETTING: An academic center. PATIENT(S): Patients with infertility who underwent endometrial biopsy for BCL6 evaluation INTERVENTION(S): Exogenous estradiol and/or progesterone. MAIN OUTCOME MEASURE(S): Endometrial BCL6 histological score (HSCORE) and overexpression (HSCORE >1.4) RESULT(S): Two hundred and forty-four patients were included in the analysis: 76 patients were sampled in a natural menstrual cycle without exogenous hormone exposure (NC), 25 under a modified natural cycle embryo transfer protocol with choriogonadotropin alfa injection followed by luteal phase vaginal progesterone supplementation (mNC), and 143 under a programmed cycle embryo transfer protocol, with estradiol administration followed by addition of intramuscular progesterone-in-oil injections (PC). Median HSCORE (interquartile range) was the highest in NC (3.0 [1.8-3.6]). BCL6 expression was significantly lower in mNC (1.1 [0.4-2.1]) and PC groups (0.8 [0.3-1.3]) compared with NC. In addition, BCL6 overexpression (HSCORE >1.4) was observed in 80.3% of NC, 40.0 % of mNC, and 23.1 % of PC. After adjusting for covariates, the endometrium exposed to exogenous progesterone had significantly lower odds of BCL6 overexpression than that of a natural menstrual cycle (adjusted odds ratio, 0.12 [95% CI 0.04-0.35] for mNC; and odds ratio, 0.08 [95% CI 0.04-0.17] for PC). CONCLUSION(S): BCL6 expression differs by the type of uterine preparation method, with lower levels observed with exogenous progesterone exposure. The validity and utility of BCL6 testing under medicated endometrial state warrants further investigation.