Roles of estradiol levels on the day of human chorionic gonadotrophin administration in the live birth of patients with frozen embryo transfer

BACKGROUND: Estradiol (E(2)) is an important hormone in women. Changes of serum E(2) levels may affect the endometrial receptivity for embryo implantation and thus affect pregnancy outcomes. This study was to assess the association between serum E(2) levels on the day of human chorionic gonadotrophin (HCG) administration and live‐birth rates in patients with frozen embryo transfer (FET). METHODS: Totally 2071 women receiving long protocols of long‐acting gonadotropin‐releasing hormone (GnRH) agonists were enrolled. According to the E(2) levels on the day of HCG administration, these patients were divided into four groups: 676 cases of E(2) ≤ 3051 pg/mL in Q(1) group, 676 cases of 3051 pg/mL < E(2) ≤ 4558 pg/mL in Q(2) group, 675 cases of 4558 pg/mL < E(2) ≤ 6718 pg/mL in Q(3) group, and 674 cases of E(2) > 6718 pg/mL in Q(4) group. The clinical indicators including female age, body mass index (BMI), duration of infertility, infertility styles, treatment protocols, hormone levels, total antral follicle count, endometrial thickness, top‐level embryos, and live‐birth rates were analyzed, and multivariable logistic model was conducted to select significant variables. RESULTS: Significant differences were observed for the female age (OR = 0.965, 95% CI: 0.946‐0.985, P < .001), total antral follicle counts (OR = 1.025, 95% CI: 1.008‐1.043, P = .004), transferring what day of embryos (OR = 1.242, 95% CI: 1.137‐1.356, P < .001), endometrial thickness (OR = 1.058, 95% CI: 1.004‐1.115, P = .035), top‐level embryos (OR = 1.416, 95% CI: 1.157‐1.731, P = .001), and E(2) levels on HCG day >6781 pg/mL (OR = 1.344, 95% CI: 1.069‐1.690, P = .011) between live‐birth and non‐live‐birth groups. The area under the curve (AUC) for E(2) levels on HCG day was 0.558, the sensitivity was 54.75%, and the specificity was 55.10%. CONCLUSION: Serum E(2) level on HCG day was an independent predictor of live‐birth achievement in patients with FET.