Previous studies have reported inconsistent associations between maternal serum ferritin concentrations and the risk of spontaneous preterm birth (sPTB). The aim of the present study was to examine the association between Fe biomarkers, including serum ferritin concentrations, and the risk of total ( 75th percentile ( ≥ 43 μg/l) (OR 1.49, 95% CI 1.06, 2.10) and >90th percentile ( ≥ 68 μg/l) (OR 1.92, 95% CI 1.25, 2.96). Increased odds of early and moderate-to-late sPTB were associated with ferritin levels >90th percentile (OR 2.50, 95% CI 1.32, 4.73) and >75th percentile (OR 1.56, 95% CI 1.03, 2.37), respectively. No association was found between the risk of sPTB and elevated sTfR levels or Fe deficiency. In conclusion, elevated maternal serum ferritin levels in early pregnancy are associated with an increased risk of sPTB from 34 weeks of gestation. The usefulness of early pregnancy ferritin levels in identifying women at risk of sPTB warrants further investigation.