Interaction between triglyceride-glucose index and body mass index on pregnancy loss in Chinese women with polycystic ovary syndrome: a secondary analysis of a randomized clinical trial

This study aims whether triglyceride-glucose Index (TyG) / body mass index (BMI) mediates associations of BMI/TyG with insulin resistance (IR), metabolic syndrome (MetS), and pregnancy outcomes and the extent of interaction or joint relations of TyG and BMI with IR, MetS, and pregnancy outcomes. This study is a secondary analysis of the Polycystic Ovary Syndrome Acupuncture and Clomiphene Trial. Eight hundred fifty-five women with PCOS were recruited from 27 hospitals in mainland China between 2012 and 2015. Mediation, interaction and joint analysed of BMI and TyG on IR, MetS and pregnancy outcomes, using generalized linear model, stepwise regression, multinomial logistic regression, and restricted cubic spline. The predictive performance of TyG + BMI for Pregnancy Loss was determined using receiver operating characteristic curve analysis. A significant interaction between BMI and TyG was observed for pregnancy loss (P < 0.05). Simple effects analysis further revealed distinct patterns across TyG strata: Within the TyG T2 tertile, pregnancy loss differed significantly between BMI < 24.0 kg/m², BMI 24.0–27.9 kg/m², and BMI ≥ 28.0 kg/m². Within the TyG T3 tertile, both BMI 24.0–27.9 kg/m² and BMI ≥ 28.0 kg/m² showed significant differences compared to BMI < 24.0 kg/m². Conversely, under BMI stratification: in the BMI ≥ 28.0 kg/m² subgroup, TyG T2 and T3 exhibited significant differences relative to TyG T1. The joint association analysis demonstrated that individuals with BMI ≥ 28.0 kg/m² and TyG T3 had substantially elevated risks compared to those with BMI < 24.0 kg/m² and TyG T1. Adjusted odds ratios (ORs) were as follows: IR (OR: 11.548, 95% CI: 3.468–38.452); MetS (OR: 46.207, 95% CI: 3.917–545.012); Ovulation (OR: 0.096, 95% CI: 0.025–0.371); Conception (OR: 0.204, 95% CI: 0.059–0.701); Clinical Pregnancy (OR: 0.196, 95% CI: 0.050–0.772). For the TyG + BMI, the AUC was 0.604 (sensitivity: 68%; specificity: 50%). Interaction was found between BMI and TyG on the prevalence of pregnancy loss. ClinicalTrials. gov NCT01573858 (2012.04.10); Chinese Clinical Trial Registry ChiCTR-TRC-12002081 (date: 2012.03.20).