Association Between Dietary Iron Intake In Early Pregnancy And The Risk Of Gestational Diabetes Mellitus

Objective: We assessed the association of dietary total iron,heme iron,and non-heme iron intake in early pregnancy with the risk of developing gestational diabetes mellitus(GDM)in pregnant women.Methods: We conducted a prospective cohort study among pregnant women who were registered in early pregnancy during November 2016 to December 2018.Sociodemographic characteristics and life-style data in early pregnancy were collected at baseline by questionnaires on site,and a validated semi-quantitative food frequency questionnaire(FFQ)was used to assess dietary iron intake(including total iron,heme iron and non-heme iron)and other food intake.GDM was diagnosed according to the oral glucose tolerance test(OGTT)in the second trimester.Participants were classified into quartiles of iron intake.Multiple Logistic regression models were used to examine the association between dietary iron intake and GDM risk,and adjust for potential confounders.Sensitivity analyses were carried out to evaluate the robustness of our findings.Results: A total of 107 incident cases of GDM were identified among 1106 pregnant women aged 18-48 in our analysis,corresponding to 9.7% of pregnant participants.The average of dietary total iron intake during early pregnancy was 17.6mg/d,heme iron and non-heme iron intake were 2.7mg/d,14.9mg/d,respectively.In the fully adjusted Logistic regression analysis(the final model was adjusted for age,BMI,family history of diabetes,parity,dietary vitamin C intake),total iron intake was significantly associated with a higher risk of GDM(OR=2.766,95%CI 1.213-6.307)for the highest versus the lowest quartile of intake.The observed associations were same for heme iron intake(OR=2.114,95%CI 1.086-4.114)and non-heme iron intake(OR=2.248,95%CI 1.027-4.922).After excluding subjects out of total energy intake below percentile 2.5 and above percentile 97.5,multivariable-adjusted ORs(95%CI)of GDM for comparisons between the highest and the lowest quartiles were 2.777 (1.169-6.595)for total iron intake,2.247(1.136-4.446)for heme iron intake,1.870(0.846-4.132)for non-heme iron intake.After excluding subjects with family history of diabetes,adjusted ORs(95% CI)of the highest versus the lowest quartile were 2.737(1.182-6.340)for total iron intake,1.942(1.005-3.752)for heme iron intake,2.620(1.167-5.883)for non-heme iron intake.Conclusions: Our overall findings suggest that higher dietary intake of total iron,heme iron and non-heme iron in early pregnancy are significantly associated with an increased risk of GDM.