OBJETIVE: To evaluate the association between the use of iron salts during the first two trimesters of gestation in non-anemic women and the development of gestational diabetes mellitus. METHODS: The study used maternal data from the 2015 Pelotas Birth Cohort. All non-anemic women at the 24th week of gestation (n = 2,463) were eligible for this study. Gestational diabetes mellitus was self-reported by women. Crude and adjusted logistic regression were performed considering level of significance = 0.05. RESULTS: Among the women studied, 69.7% were exposed to prophylactic iron supplementation in the first two trimesters of gestation. The prevalence of gestational diabetes mellitus among those exposed was 8.7% (95%CI: 7.4–10.1) and 9.3% (95%CI: 7.4–11.6) among those who were not exposed. Iron supplementation was not associated with increased risk of gestational diabetes mellitus in crude (OR = 0.9; 95%CI: 0,7–1,3) and adjusted analysis (OR = 1.1; 95%CI :0,8–1,6). CONCLUSIONS: The results suggest that routine iron use in non-anemic pregnant women does not increase the risk of developing gestational diabetes. This evidence supports the existing national and international guidelines, in which prophylactic iron supplementation is recommended for all pregnant women as soon as they initiate antenatal care in order to prevent iron deficiency anemia.