Effect of High Serum Estradiol Levels and Duration of Vaginal Estradiol Administration on Reproductive Outcomes in Frozen-Thawed Embryo Transfer Cycles

Background: The purpose of this study is to assess the effects of high serum estradiol (E2) levels on reproductive outcomes as well as to compare pregnancy outcomes of duration of vaginal E2 administration after the day of progesterone (P4) initiation in frozen-thawed embryo transfer (FET) hormonal replacement cycles. Methods: We performed a retrospective cohort study on 627 patients <= 40 years old that underwent a FET cycle. The patients were grouped based on the serum E2 level on the P4 initiation day as follows: E2 <= 600 pg/mL (n = 471); E2 >= 900 pg/mL (n = 151); the group of E2 600-900 pg/mL (n = 5) was not included in the analysis due to too small sample size. A total of 151 patients with E2 >= 900 pg/mL were grouped based on the duration of vaginal E2 administration after the day of P4 initiation: withdrawal before transfer (n = 53); constant administration (n = 98). Results: There was no significant difference in implantation rate, clinical pregnancy rate, spontaneous abortion rate, premature birth rate, live birth rate and multiple pregnancy rate between the two E2 level groups. The logistic regression analysis demonstrated that age was the only variable that significantly affected clinical pregnancy rate and live birth rate. There were no fetal malformations in either group. Baseline characteristics of patients with different duration of vaginal E2 administration were similar. The pregnancy outcomes showed no significant difference between the withdrawal before transfer group and the constant administration group. Conclusions: In FET cycles, high E2 level on the embryo transfer day did not reduce the clinical pregnancy and live birth rates. In addition, vaginal E2 could be stopped on the embryo transfer day since we found no benefit in continuing E2 until the pregnancy testing day.