Association between body fat indices and female infertility: A cross-sectional study

Excess body fat and its distribution are known to influence female reproductive function; however, the relationship between emerging body fat-related indices and infertility remains insufficiently explored. This study aimed to investigate the association between the Conicity Index (C-index), Relative Fat Mass (RFM), and Metabolic Score for Visceral Fat (METS-VF) and infertility among women of reproductive age in the United States. The study included women aged 18 to 45 years and assessed infertility using the National Health and Nutrition Examination Survey question RHQ074 on reproductive health. Multivariable logistic regression, adjusted for confounders, was used to analyze the association between body fat indices and infertility risk. Receiver operating characteristic curve analysis was conducted to evaluate each metric's predictive strength. Of 1103 women, 132 reported infertility. Infertile women had higher C-index (1.3 vs 1.27), RFM (43 vs 40), and METS-VF (8.24 vs 7.37) than fertile women. Each 1-unit increase in these indices was associated with higher odds of infertility (C-index odds ratio [OR] = 2.73, RFM OR = 1.07, METS-VF OR = 1.28). METS-VF had the highest predictive value (area under the curve = 0.65), as confirmed by random forest analysis. Positive associations between infertility and C-index, RFM, and METS-VF suggest that these indices could help assess infertility risk and support targeted reproductive health interventions.