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 ( < 37 weeks), early ( < 34 weeks) and moderate-to-late (34–36 weeks) sPTB. The study cohort included 2254 women with singleton pregnancies attending first-trimester screening in New South Wales, Australia. sPTB included births following spontaneous labour or preterm premature rupture of the membranes. Serum collected at a mean gestational age of 12·0 (sd 0·9) weeks was analysed for Fe biomarkers, including serum ferritin and soluble transferrin receptor (sTfR), and the inflammatory biomarker C-reactive protein. Multivariate logistic regression analysis evaluated the association between low and high Fe levels and sPTB. Women with elevated serum ferritin concentrations were more likely to be older, nulliparous or have gestational diabetes. The multivariate analysis found increased odds of sPTB for women with elevated ferritin levels defined as >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.