Association between endogenous oxytocin levels and live birth rates following fresh embryo transfer: a prospective cohort study

Objective To investigate the associations between serum and follicular fluid oxytocin levels and live birth rate (LBR) in IVF cycles, and to examine their correlations with clinical parameters. Design Prospective cohort study. Methods A total of 680 infertile patients undergoing IVF cycles between October 2024 and January 2025 were enrolled for serum and follicular fluid oxytocin measurement. The associations between serum and follicular fluid oxytocin levels and LBR were assessed using three statistical approaches: multivariable logistic regression, inverse probability weighting, and a double robust model. Smoothed curve fitting was employed to explore the relationships between oxytocin levels and LBR. Additionally, Spearman correlation analysis was performed to examine the associations between oxytocin levels and key clinical parameters. Results Serum oxytocin demonstrated a negative linear association with LBR (p-nonlinear = 0.911), whereas follicular fluid oxytocin showed a positive association (p-nonlinear = 0.425). In the double robust model, each 100 pg/mL increase in serum oxytocin decreased the likelihood of live birth by 37% (95% CI: 25%–47%), whereas a corresponding increase in follicular fluid oxytocin improved it by 18% (95% CI: 2%–37%). Additionally, serum oxytocin correlated positively with triglycerides (r = 0.294), LDL-C (r = 0.165), and insulin (r = 0.257), but negatively with HDL-C (r = –0.167). Conversely, follicular fluid oxytocin correlated positively with ovarian response markers, including hCG-trigger day estradiol (r = 0.229) and oocytes retrieved (r = 0.248). Conclusion Higher basal serum oxytocin prior to ovarian stimulation is negatively associated with LBR following fresh embryo transfer, whereas elevated follicular fluid oxytocin correlates with improved ovarian response.