Determining the Association between Serum Estradiol Levels on hCG Trigger Day and Live Birth Rates in Non-PCOS Patients

This study aims to retrospectively analyze the association of serum estradiol (E2) levels on human chorionic gonadotropin (hCG) trigger day and live birth rates (LBRs) in women undergoing fresh embryo transfer and not exhibiting polycystic ovary syndrome. A total of 13,950 patients who had fresh embryo transfer between December 2013 and December 2019 were included. LBR served as the key outcome indicator. After controlling for variables, a multivariable regression analysis revealed a significant relationship between serum E2 levels on the hCG trigger day and LBR [relative risk (RR) 1.027, 95% confidence interval (CI) 1.007, 1.049]. Stratification analysis revealed thatthe LBR was positively associated (RR 1.052, 95% CI 1.004, 1.102) with every 1 ng/mL increase of serum E2 on the hCG trigger day for the subgroup with low antral follicle counts on the trigger day. In particular, a two-piecewise linear regression model demonstrated that when blood E2 content was less than 2.1 ng/mL, there was a positive correlation (RR 1.188, 95% CI 1.057, 1.334) between serum E2 and LBR with every increment of 1 ng/mL E2. However, the relationship between E2 levels and LBR was not statistically significant (RR 1.002, 95% CI 0.971, 1.032) when the level of E2 was higher than the 2.1 ng/mL inflection point. Further prospective studies are required to explore the possible mechanisms and to consolidate the association between serum E2 levels on the hCG trigger day and LBR.