Association between Body Roundness Index and infertility risk in Han Chinese women: a retrospective observational study

Background Infertility is a major global health concern and is increasingly recognized to be influenced by metabolic and anthropometric factors. The Body Roundness Index (BRI), a waist- and height-based indicator of central adiposity, has been associated with cardiometabolic outcomes. Although emerging studies have examined the relationship between BRI and infertility, evidence remains limited across populations, particularly regarding non-linear associations and effect modification. Objective This study aimed to examine the association between BRI and infertility risk in Han Chinese women and to explore potential non-linear and subgroup-specific patterns. Methods We conducted a retrospective observational study including 425 Han Chinese women aged 20–44 years. BRI was calculated from measured waist circumference and height. Infertility was defined as failure to conceive after 12 months of unprotected intercourse. Multivariable logistic regression was used to evaluate the association between BRI and infertility after adjustment for selected confounders, including age, Body Mass Index, physical activity, and Polycystic Ovary Syndrome. Restricted cubic spline functions within logistic regression were applied to assess potential non-linear relationships, and subgroup analyses were performed to evaluate effect modification. Results Women with infertility had significantly higher BRI values than those without infertility (8.5 ± 2.0 vs. 7.1 ± 1.5, p < 0.001). After multivariable adjustment, each unit increase in BRI was associated with higher odds of infertility (adjusted OR = 1.38, 95% CI: 1.22–1.56). Restricted cubic spline analysis demonstrated a non-linear dose-response relationship, with infertility risk increasing more steeply at BRI levels above approximately 8.0. Stronger associations were observed among women aged 35–44 years, those with higher BMI, sedentary lifestyles, Polycystic Ovary Syndrome, or lower income ( p for interaction