Are the estrogen levels on the day of frozen-thawed embryo transfer related to the outcomes in hormonal replscement treatment cycles?

Objective: To investigate the impact of estrogen (E-2) levels on the day of embryo transfer on pregnancy outcomes of frozen-thawed embryo transfer (FET) in hormonal replacement treatment (HRT) cycles. Methods: A total 193 HRT cycles was retrospectively identified. Cycles were divided into two groups: high E-2 group (>150 pg/ ml) and low E-2 groups (<= 150 pg/ml). Stimulation and embryological characteristics were compared between the two groups. Result(s): Regarding the E-2 levels on the day of frozen-thawed embryo transfer, no significant differences were found in clinical pregnancy rate between high E-2 groups and low E-2 groups in both Day 3 or Day 5 embryotransfer subgroups (P>0.05). The logistic regression analysis revealed that E-2 levels on the day of embryo transfer were not independently associated with positive clinical pregnancy (Day 3 embryo-transfer subgroup: OR = 1.004, 95% CI: 0.997-1.011, P = 0.237; Day 5 embryo-transfer subgroup: OR = 1.001, 95% CI 0.994-1.09, P = 0.761), and the areas under the receiver operating characteristic curve examining were 0.551 in Day 3 embryo-transfer subgroup and were 0.556 in Day 5 embryo-transfer subgroup. Conclusion(s): The concentration of serum E-2 on the day of embryo transfer cannot serve as an indicator to predict the outcomes of artificial FET cycles.