The objective was to evaluate the effect of anemia during pregnancy on the risk of dental caries development in pregnant women. A prospective cohort including a sample of pregnant women in a prenatal care unit of São Luís, Brazil, was done. The incidence of dental caries during pregnancy, according to Nyvad's criteria, was the outcome. The main independent variables were serum iron, ferritin, hemoglobin, erythrocyte, hematocrit, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), and red cell distribution width (RDW). Pregnant women (n = 121) were evaluated at two moments: up to 16th week of gestational age (T1) and in the last trimester of pregnancy (T2). Crude and adjusted associations were estimated by the incidence ratio risk (IRR) and respective 95% confidence intervals (95%CI). After adjustment, higher serum concentrations of ferritin (IRR = 0.97, 95%CI 0.95-0.99) in T1, and Fe (IRR = 0.99, 95%CI 0.98-0.99), ferritin (IRR = 0.99, 95%CI 0.98-0.99), erythrocyte (IRR = 0.71, 95%CI 0.50-0.99), hemoglobin (IRR = 0.84, 95%CI 0.73-0.96), hematocrit (IRR = 0.93, 95%CI 0.88-0.98), MCV (IRR = 0.91, 95%CI 0.86-0.96), and MCH (IRR = 0.83, 95%CI 0.74-0.93) in T2, were associated with fewer incidence of dental caries in pregnant women. Iron deficiency anemia during pregnancy is a risk factor for the incidence of dental caries in these women.