Maternal Iron Intake During Pregnancy and Gestational Diabetes Mellitus: A Prospective Cohort Study

Abstract

ObjectivesConcerns relative to excessive iron intake are raised when high iron status exposure has been linked in observational studies to a greater risk of gestational diabetes mellitus (GDM). We aimed to examine the association between iron intake during pregnancy and GDM risk in Chinese women. MethodsThe study included 2174 pregnant women from the Tongji Maternal and Child Health Cohort (TMCHC), a prospective cohort in Wuhan, China. Iron intakes from food and supplementation prior to GDM diagnosis were assessed using a validated food frequency questionnaire (FFQ) and a detailed supplement questionnaire collected at 13–28 weeks of gestation. GDM was ascertained by an oral glucose tolerance test at 24–28 weeks of gestation. Odd ratios (ORs) of GDM in relation to categories of iron intake (i.e., quartiles of total and food iron intake, categories of supplemental iron intake [0, 0–30, >30 mg/day]) were estimated using logistic regression models, with adjustment for demographic, dietary and lifestyle factors. ResultsA total of 242 (11.1%) women were diagnosed with GDM. The adjusted ORs (95% CIs) for the risk of GDM associated with the higher quartiles compared with the lowest quartile of total iron intake were 1.44 (0.89, 2.33), 2.03 (1.27, 3.25), and 2.86 (1.84, 4.43), respectively (P for trend < 0.001). This association was entirely driven by supplemental iron intake. Women with supplemental iron intake > 30 mg/day during pregnancy had an OR for GDM of 2.32 (95% CI: 1.60, 3.36). Moreover, the significant positive effect of supplemental iron was mainly attributed to iron supplementation during mid-pregnancy (≥60 vs. 0 mg/day, OR: 1.46, 95% CI: 1.00, 2.13), while no effect of iron supplementation during early pregnancy was observed. No significant association was found between food iron intake and GDM. ConclusionsHigher supplemental iron intake during pregnancy was significantly associated with elevated GDM risk. Adverse effect of indiscriminate iron supplementation, especially inappropriate supplementation during mid-pregnancy, would likely outweigh benefits for maternal health. Funding SourcesFunding was received from the National Natural Science Foundation of China (NSFC81673159), National Program on Basic Research Project of China (NO.2013FY114200) and the Fundamental Research Funds for the Central Universities (HUST 2019kfyXMPY008) (Nianhong.Yang.).