Decreasing serum estradiol level on day of progesterone start in programmed frozen embryo transfer cycles and the pregnancy outcomes.

High serum estradiol levels may reduce the success of conception and live birth in both in vitro fertilization and frozen embryo transfer (FET). This retrospective study sought to determine whether an association exists between decreasing the serum estradiol level and the clinical outcome following programmed FET cycles. The analysis retrieved the data of patients who underwent programmed FET cycles at the Center of Reproductive Medicine of Weifang People's Hospital from January 2022 to March 2023. The pregnancy outcomes were compared between patient groups with different estradiol levels but otherwise identical profiles. Of all 769 included patients, 188 received 3 mg/d estradiol valerate (group A) and 581 received 4 mg/d 17β-estradiol (group B). Of group B patients, 186 (group BP) with identical baseline clinical data as patients in group A were selected by using propensity score matching. While the serum estradiol level was much lower in those receiving 3 mg/d estradiol valerate (group A) than those receiving 4 mg/d 17β-estradiol (group BP), the endometrial thickness was not affected by the medication regimen. Both groups had comparable pregnancy outcomes, including clinical pregnancy, implantation, early miscarriage, ectopic pregnancy, and live birth rate. In programmed FET cycles, decreasing the serum level of estradiol does not significantly impact the pregnancy outcome.