The association between triglyceride glucose-body mass index and live birth outcomes in women with clinical pregnancy after frozen-thawed embryo transfer: a cohort study

Metabolic syndrome is common among infertile women and is closely related to insulin resistance (IR). Triglyceride glucose-body mass index (TyG BMI) is a newly explored indicator of IR. Currently, the association between TyG BMI and live birth outcomes has been studied in women with polycystic ovary syndrome (PCOS) undergoing in vitro fertilization (IVF), However, there is a lack of research on the general population of frozen-thawed embryo transfer (FET). This is a cohort study based on data from a reproductive center in China from January 2016 to December 2023. The association between TyG BMI and live birth outcomes in women with clinical pregnancy after FET was evaluated using generalized additive model(GAM) and threshold saturation effect analysis. A total of 3,709 cycles resulted in clinical pregnancy after FET, with a mean age of 32.76 ± 3.99 years. Among these, 2860 cycles (77.11%) resulted in live births, with a mean age of 32.46 ± 3.81 years. After adjusting for confounding factors, TyG BMI was negatively correlated with live birth outcomes (OR = 0.994, 95% CI: 0.992, 0.996; p < 0.001). GAM analysis showed that the smooth term of TyG BMI was significant (p < 0.001), indicating a nonlinear relationship. Threshold effect analysis identified a breakpoint (K) of 176.849 (95% CI: 168.097, 186.702). When TyG BMI was below 176.849, The increase in the live birth rate was not significant, but when TyG BMI exceeded 176.849, for each additional unit, the chance of a live birth decreases by approximately 0.8% (OR = 0.992, p < 0.001). Our findings suggest that a higher TyG BMI is negatively associated with live birth outcomes in women with clinical pregnancy after FET. Further research is needed to validate these findings.