Effect of the Trends of Estradiol Level on the Outcome of in Vitro Fertilization-embryo Transfer With Antagonist Regimens: a Single Center Retrospective Cohort Study

Background: The outcome of in vitro fertilization-embryo transfer is often determined according to follicles and estradiol levels following gonadotropin stimulation. However, there is no accurate indicator to predict pregnancy outcome, and it has not been determined how to choose subsequent drugs and dosage based on the ovarian response. This study aimed to make timely adjustments to follow-up medication to improve clinical outcomes based on the potential value of estradiol growth rate. Methods: Serum estradiol levels were measured on the day of gonadotrophin treatment (Gn0), four days later (Gn4), seven days later (Gn7), and on the trigger day (HCG). The ratio was used to determine the increase in estradiol levels. According to the ratio of estradiol increase, the patients were divided into four groups: group A1 (Gn4/Gn0≤6.44), group A2 (6.44˂Gn4/Gn0≤10.62), group A3 (10.62˂Gn4/Gn0≤21.33), and group A4 (Gn4/Gn0>21.33); group B1 (Gn7/Gn4≤2.39), group B2 (2.39˂Gn7/Gn4≤3.03), group B3 (3.03˂Gn7/Gn4≤3.84), and group B4 (Gn7/Gn4>3.84). We analyzed and compared the relationship between data in each group and pregnancy outcome. Results: In the statistical analysis, the estradiol levels of Gn4 (P = 0.029, P = 0.042), Gn7 (P< 0.001, P = 0.001), and HCG (P< 0.001, P = 0.002), as well as the ratios of Gn4/Gn0 (P = 0.004, P = 0.006), Gn7/Gn4 (P = 0.001, P = 0.002), and HCG/Gn0 (P< 0.001, P< 0.001) both had clinical guiding significance, and the lower one significantly reduced the pregnancy rate. The outcomes were positively linked to groups A (P = 0.040, P = 0.041) and B (P = 0.015, P = 0.017). The logistical regression analysis revealed that group A1 (OR = 0.440 [0.223–0.865]; P = 0.017, OR = 0.368 [0.169–0.804]; P = 0.012) and B1 (OR = 0.261 [0.126–0.541]; P< 0.001, OR = 0.299 [0.142–0.629]; P = 0.001) had opposite influence on outcomes. Conclusion: Maintaining a serum estradiol increase ratio at least above 2.39 on Gn7/Gn4 may result in a higher pregnancy rate. When estradiol growth is not ideal, gonadotrophin dosage should be adjusted appropriately to ensure the desired outcome.