Association between relative fat mass and female infertility among reproductive-aged women from NHANES 2013–2020

Female infertility is a prevalent condition closely linked with obesity. Current evaluation metrics like body mass index (BMI) and waist circumference (WC) have limitations. Relative fat mass (RFM) is a newer, more accurate obesity metric, but its relationship with infertility lacks research. Data from 3489 female participants aged 18-45 years from the NHANES 2013-2020 cycles were extracted and analyzed. Infertility was assessed based on participants' pregnancy attempts and medical consultations. The primary exposure variables were BMI, WC, and RFM. Survey-weighted logistic regression models were conducted to compare their associations with infertility, expressed as odds ratios (ORs). RFM was further categorized into quartiles for additional regression analysis. Subgroup analyses were conducted to evaluate whether the association between RFM and infertility differs across key demographic and clinical factors, including age, race, PIR, education level, BMI, smoking status, DM, hypertension, age at menarche, and history of pelvic inflammatory disease (PID). Restricted cubic splines (RCS) were employed for robustness and linearity assessments. Our results showed an infertility prevalence of 13.41%, with affected women being older and having higher BMI. The OR (1.039, 95% CI: 1.010, 1.068) for RFM in regression analysis of fully adjusted Model was higher than for BMI (1.020, 95% CI: 1.002, 1.039) and WC (1.014, 95% CI: 1.006, 1.022), indicating that each unit increase in RFM correlates with a higher risk of infertility. Similarly, quartile analysis of fully adjusted Model indicated increased infertility risk with higher RFM quartiles (Q2: OR = 1.66, 95% CI: 1.05, 2.64; Q3: OR = 1.79, 95% CI: 1.16, 2.74; Q4: OR = 2.23, 95% CI: 1.38, 3.60). Additionally, results were consistent in the supplementary subgroup analysis without interaction, and RCS confirmed a linear relationship. Our findings demonstrate a significant association between RFM and female infertility in a population-based sample, supporting the hypothesis that excess adiposity may play a role in reproductive health. Further research is needed to explore the mechanisms and broader applications of RFM in female reproductive health.