Objective To explore the association between total iron， iron supplements， dietary total iron， heme iron intake and the risk of gestational diabetes mellitus（GDM）.
Methods A total of 668 pregnant women who gave birth in one hospital in Shanghai during January 2020 to July 2021 were included in a retrospective cohort study. Baseline characteristics and data of iron supplements in second trimester were collected through a questionnaire. A simplified dietary frequency questionnaire was used to quantify the food intake in second trimester. Total iron， iron supplements， dietary total iron， and heme iron intake was classified into groups by quintile and median. The association between iron intake from different sources and risk of GDM was determined using logistic regression analysis.
Results After correction for age， family history of diabetes， overweight / obesity before pregnancy， hemoglobin（Hb）in first trimester， energy， carbohydrate energy， protein， and free sugar， it showed no association between total iron intake and risk of GDM （P>0.05）， while elevated risk of GDM among women with high iron supplements intake （OR=1.65； 95%CI： 1.14‒2.39）， and decreased risk of GDM among those with high dietary total iron intake （OR=0.53； 95%CI： 0.35‒0.81）. However， no association was found between heme iron intake and risk of GDM （P>0.05）.
Conclusion High dietary total iron intake may be a protective factor， while high iron supplements may be a risk factor for GDM. It suggests that pregnant women should carefully choose high-dose iron-containing supplements in the absence of iron deficiency， as dietary iron intake should be the priority.
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