The Cardiometabolic Index: A Novel Predictor of Insulin Resistance and Adverse Reproductive Outcomes in Polycystic Ovary Syndrome

Background Polycystic ovary syndrome (PCOS) is a prevalent endocrine disorder characterized by concurrent reproductive and metabolic dysfunction, with insulin resistance (IR) serving as a core pathophysiological driver. The Cardiometabolic Index (CMI), which integrates the waist-to-height ratio (WHtR) and the triglyceride-to-high-density lipoprotein cholesterol (TG/HDL-C) ratio, has emerged as a potential composite marker of metabolic health. Its associations with IR and reproductive outcomes in PCOS, however, remain insufficiently characterized. Methods This secondary analysis included data from 944 women with PCOS enrolled in the multicenter PCOSAct trial. The association between CMI and IR was assessed using multivariate logistic regression, with average marginal effects calculated to quantify risk contribution. Nonlinear relationships were evaluated with restricted cubic splines. Subgroup analyses were performed to examine effect modification. Time-to-event outcomes (ovulation and live birth) were analyzed via Kaplan-Meier curves and Cox proportional hazards models, adjusting for age and treatment allocation. Results A significant positive association was observed between CMI and the risk of IR in PCOS. After adjustment for potential confounders, higher CMI were at an increased risk of IR (OR: 1.88, 95% CI: 1.59–2.23). A nonlinear dose-response relationship was identified, with an inflection point at a CMI of 1.01. Subgroup analyses demonstrated consistent associations across most demographic and clinical strata, although the relationship was attenuated in patients with HA. Furthermore, elevated CMI levels were significantly associated with reduced cumulative ovulation rates ( P  = 0.014) and lower probabilities of live birth ( P  = 0.002). Conclusions CMI serves as a robust, independent predictor of IR in women with PCOS, demonstrating a nonlinear threshold effect. It is also correlated with poorer reproductive outcomes. These findings suggest CMI's potential utility as a practical clinical tool for the early assessment of metabolic risk and for informing personalized management strategies in this population.