High level of estrogen on the day before embryo transfer is associated with reduced live birth after frozen embryo transfer: a retrospective cohort study from 14565 cycles.

BACKGROUND: The endometrial preparation of frozen embryo transfer cycle is to synchronize of endometrium and embryo under the condition of exogenous estrogen and progesterone drugs in HRT or follicle monitoring in NC. Estrogen and progesterone are crucial and different hormone levels could imply variations on endometrial preparation. The effect of estrogen and progesterone levels before the embryo transfer on the live birth is still controversial. METHODS: This was a retrospective cohort study involving all infertile women who had undergone freeze-all and first frozen-embryo transfer cycle with HRT or NC in the period from January 2016 to December 2020 at a tertiary care center. Deciles and receiver operating characteristic curves were used to determine the cutoff values for estrogen and progesterone levels on the day before embryo transfer. Multivariate logistic regression was performed to analyze the independent effect of estrogen and progesterone on live birth. RESULTS: The cutoff value of estrogen level on the day before embryo transfer in the HRT group was 903.10 pg/mL. The lower level of estrogen on the day before embryo transfer in the HRT group corresponded to a higher live birth rate (51.4% vs. 32.9%, P < 0.001). The cutoff value of estrogen level on the day before embryo transfer in the NC group was 194.40 pg/mL. The lower level of estrogen in the NC group corresponded to a higher live birth rate (53.0% vs. 48.6%, P < 0.001). After adjusting for the possible confounders, estrogen level was the independent influencing factor of the live birth in both HRT and NC, with the odds ratios of 0.56 (0.45, 0.70) and 0.85 (0.76, 0.95), respectively. Progesterone levels had no effect on live birth in either HRT or NC after adjusting for confounders. CONCLUSIONS: In freezing-all cycles, the higher estrogen level on the day before embryo transfer may reduce the live birth rate in HRT and NC.