Nonlinear relationship between serum LH levels on hCG trigger day and live birth rates in patients with fresh embryo transfer: a retrospective cohort study

Abstract

In assisted reproductive technology (ART), the assessment of sex hormones is indispensable. Maintaining an appropriate level of luteinizing hormone (LH) is crucial for ovarian and endometrial development. However, the relationship between LH concentrations on the hCG trigger day and pregnancy outcomes after fresh embryo transfer (ET) remains relatively unclear. The aim of our study was to explore the role of serum LH levels in live birth rates (LBRs) and its specific relationship. We conducted a retrospective analysis of 9,044 patients who underwent fresh embryo transfer from 2019 to 2024. A multivariate regression model was used to identify the relationship. Stratification analysis was performed to test for effect modification in subgroups. The generalized additive model (GAM) and two-piecewise model were employed to describe the nonlinear relationship. We found a positive relationship between serum LH levels and LBRs when LH concentrations were lower than 4.31 mIU/ml (odds ratio [OR] = 1.06, 95% confidence interval [CI] = 1.00-1.12, P = 0.042). No significant relationship was observed when LH concentrations were higher than 4.31 mIU/ml. In the exploratory subgroup analyses, the similar association was identified in GnRH agonist cycles, with an inflection point at 4.09 mIU/mL. The significant interaction was also identified between infertility type and serum LH levels in relation to LBRs. Our research found the nonlinear relationship between serum levels on the hCG trigger day and LBRs. We tentatively identified an inflection point at 4.31 mIU/ml, and further studies are warranted to validate its potential clinical utility.