Association of dietary iron intake and serum iron with self-reported history of pregnancy loss among women: a cross-sectional study based on NHANES 2005–2018

Abnormal iron metabolism has been suggested to be associated with pregnancy loss. However, dietary iron intake and serum iron levels reflect different aspects of iron metabolism, and their respective relationships with pregnancy loss remain unclear. This study aimed to investigate the associations of dietary iron intake and serum iron levels with self-reported history of pregnancy loss among women aged 20–50 years using data from the National Health and Nutrition Examination Survey (NHANES) 2005–2018. Analyses were conducted based on the NHANES 2005–2018 dataset. Weighted logistic regression models were applied to examine the relationships between dietary iron intake, serum iron concentrations, and the prevalence of self-reported history of pregnancy loss. Restricted cubic spline regression was utilized to characterize the dose‑response associations among these indicators. Additionally, subgroup stratification analysis and sensitivity analysis were further carried out to verify the stability and reliability of the findings. A total of 3,417 women aged 20–50 years were included in the final analysis. In the fully adjusted weighted logistic regression model, dietary iron intake was negatively associated with self-reported history of pregnancy loss (OR = 0.975, 95% CI: 0.953–0.999, P = 0.038), whereas serum iron levels were positively associated with self-reported history of pregnancy loss (OR = 1.028, 95% CI: 1.007–1.049, P < 0.001). Restricted cubic spline analysis revealed a linear negative association between dietary iron intake and self-reported pregnancy loss (P overall < 0.001) and a linear positive association between serum iron levels and self-reported pregnancy loss (P overall = 0.003). Subgroup analysis, showed a significant interaction between oral contraceptive use history and serum iron levels (P for interaction = 0.016). Sensitivity analyses supported the robustness of the findings. This cross‑sectional investigation enrolled American women aged 20–50 years. The results indicated that dietary iron intake was inversely correlated with self-reported history of pregnancy loss, whereas serum iron concentrations displayed a positive correlation with such medical history, presenting opposite association trends. A notable interactive effect was identified between oral contraceptive use history and serum iron levels. Given the inherent limitations of the cross‑sectional design, causal inference could not be established in the present study. Further prospective cohort studies are therefore required to corroborate these observations.