Association of maternal serum ferritin stratification with metabolic phenotypes and pregnancy outcomes: a single-center retrospective observational study

This study aimed to systematically investigate the associations of maternal serum ferritin (SF) stratification with lipid metabolism markers, including triglycerides (TG) and total cholesterol (CH); glucose metabolism markers, including glycated hemoglobin (HbA1c) and abnormal glucose tolerance; coagulation/vascular-related markers, including D-dimer and homocysteine (HCY); and vitamin D status, assessed by 25-hydroxyvitamin D [25(OH)D]. Complete blood count-related parameters and pregnancy outcomes were also incorporated to provide evidence for identifying metabolic phenotypes and supporting risk assessment during pregnancy. This retrospective study included 1,606 singleton pregnant women who underwent antenatal care between January 2023 and October 2024. Participants were categorized into three groups according to SF levels: low ferritin group (SF < 15 µg/L, n = 609), intermediate ferritin group (15 ≤ SF < 30 µg/L, n = 422), and relatively high ferritin group (SF ≥ 30 µg/L, n = 575). Between-group differences were assessed using the Kruskal–Wallis test, and correlations among biomarkers were evaluated using Spearman correlation analysis. Multivariable linear regression and logistic regression models were used to adjust for potential confounders, including age, body mass index (BMI), gravidity, and complete blood count-related parameters, including WBC, NLR, PLT, Hb, MCV, and RDW-SD. The low SF group showed higher levels of TG (2.84 vs. 1.78 mmol/L), CH (5.94 vs. 4.82 mmol/L), D-dimer (1.76 vs. 1.54 mg/L), and HCY (7.31 vs. 6.36 µmol/L), together with lower 25(OH)D levels (15.05 vs. 16.96 ng/mL), compared with the SF ≥ 30 µg/L group. In fully adjusted models, compared with the SF < 15 µg/L group, the SF ≥ 30 µg/L group remained associated with lower TG, CH, D-dimer, and HCY levels and higher 25(OH)D levels. The prevalence of abnormal glucose tolerance increased across SF categories (18.4%, 24.6%, and 32.0%, respectively). After full adjustment, the SF ≥ 30 µg/L group still had a significantly higher risk of abnormal glucose tolerance (OR = 2.13, 95% CI: 1.58–2.87, P < 0.001). Sensitivity analyses using alternative SF cut-offs, excluding participants in the highest 5% of NLR, excluding participants with BMI < 15 kg/m², and applying log-transformation to skewed variables showed generally consistent directions of the main findings. Exploratory analyses of pregnancy outcomes suggested that the SF ≥ 30 µg/L group had higher risks of preterm birth and hypertensive-related diagnoses and slightly lower birth weight, whereas the prevalence of GDM diagnosis and macrosomia did not differ significantly across the three groups. SF stratification may help identify distinct metabolic phenotypes during pregnancy. Low SF status was more likely to be accompanied by higher lipid, D-dimer, and HCY levels and lower 25(OH)D levels, whereas relatively higher SF status was associated with an increased risk of abnormal glucose tolerance. This retrospective observational study is hypothesis-generating and does not support causal inference or direct intervention recommendations. Future studies incorporating OGTT glucose values at each time point and abnormality patterns, inflammatory markers, comprehensive iron metabolism indicators, and prospective pregnancy outcome data are needed to further validate the clinical value of SF stratification in metabolic risk assessment during pregnancy.