Nonlinear association of serum luteinizing hormone on hCG trigger day with cumulative live birth in IVF cycles: secondary analysis of a randomized clinical trial.

PURPOSE: To investigate the impact of serum luteinizing hormone (LH) levels on the day of human chorionic gonadotropin (hCG) trigger on cumulative live birth in women undergoing in vitro fertilization (IVF) cycles.

METHODS

This was a secondary analysis of a multicenter randomized controlled trial (NCT03118141). A total of 1212 infertile women undergoing their first IVF cycle with a good prognosis for live birth were included. Participants were stratified into three groups according to tertiles of serum LH levels on the hCG trigger day (hLH): low-hLH (< 1.28 IU/L), medium-hLH (1.28-3.26 IU/L), and high-hLH (> 3.26 IU/L). Logistic regression and restricted cubic spline models were used to evaluate associations, adjusting for maternal age, body mass index, and baseline hormones.

RESULTS

Compared to the medium-hLH group, the low-hLH group exhibited significantly lower cumulative clinical pregnancy and live birth rates, along with a higher biochemical pregnancy loss rate (P < 0.05). The high-hLH group demonstrated a reduced cumulative live birth rate, while other pregnancy outcomes were comparable to the medium-hLH group. A restricted cubic spline analysis revealed a significant nonlinear, inverted U-shaped relationship between serum hLH levels and cumulative live birth rates, with the optimal threshold around 1.95 IU/L. Stratified analysis indicated that the impact of hLH levels was more pronounced in women undergoing GnRH antagonist protocols.

CONCLUSIONS

Serum hLH levels exhibit a nonlinear association with cumulative live birth rates in IVF cycles, highlighting 1.95 IU/L as a potential threshold. Individualized adjustment of hLH levels may improve pregnancy outcomes, especially in GnRH antagonist protocols.