BACKGROUND: Iron deficiency is common during pregnancy. Experimental animal studies suggest that it increases cardiovascular risk in the offspring. OBJECTIVE: To examine the relationship between maternal pregnancy dietary and supplement iron intake and hemoglobin, with offspring's arterial stiffness (measured by carotid-radial pulse wave velocity), endothelial function (measured by brachial artery flow mediated dilatation), blood pressure, and adiposity (measured by body mass index), test for mediation by cord ferritin, birth weight, gestational age, and child dietary iron intake, and for effect modification by maternal vitamin C intake and offspring sex. DESIGN: Prospective data from 2958 mothers and children pairs at 10 years of age enrolled in an English birth cohort, the Avon Longitudinal Study for Parents and Children (ALSPAC), was analysed. RESULTS: 2639 (89.2%) mothers reported dietary iron intake in pregnancy below the UK reference nutrient intake of 14.8 mg/day. 1328 (44.9%) reported taking iron supplements, and 129 (4.4%) were anemic by 18 weeks gestation. No associations were observed apart from maternal iron intake from supplements with offspring systolic blood pressure (-0.8 mmHg, 99% CI -1.7 to 0, P = 0.01 in the sample with all relevant data observed, and -0.7 mmHg, 99% CI -1.3 to 0, P = 0.008 in the sample with missing data imputed). CONCLUSION: There was no evidence of association between maternal pregnancy dietary iron intake, or maternal hemoglobin concentration (which is less likely to be biased by subjective reporting) with offspring outcomes. There was a modest inverse association between maternal iron supplement intake during pregnancy with offspring systolic blood pressure at 10 years.