High maternal iron status, dietary iron intake and iron supplement use in pregnancy and risk of gestational diabetes mellitus: In-house study and systematic review

Background: High iron measured using dietary and serum biomarkers have been associated with type 2 diabetes; however it is uncertain whether a similar association exists for gestational diabetes mellitus (GDM). Objectives: To conduct a cohort study examining first trimester body iron stores and subsequent risk of GDM and to include these findings in a systematic review of all studies examining the association between maternal iron status, iron intake (dietary and supplemental) and the risk of GDM. Methods: Serum samples for women with first trimester screening were linked to birth and hospital records for data on maternal characteristics and GDM diagnosis. Blood was analysed for ferritin, soluble transferrin receptor (sTfR) and C-reactive protein (CRP). Associations between iron biomarkers and GDM were assessed using multivariate logistic regression. A systematic review and meta-analysis, registered with PROSPERO (CRD42014013663) included all studies published in English from Jan 1995 to March 2014 that examined the association between iron and GDM and included an appropriate comparison group. Results: Of 3, 776 women, 3.4% subsequently developed GDM. Adjusted analyses found increased odds of GDM for ferritin (OR 1.41; 95% CI: 1.11, 1.78) but not for sTfR (OR 1.00, 95% CI: 0.97, 1.03) levels. Two trials of iron supplementation in early pregnancy found no association with GDM. Increased risk of GDM was associated with higher levels of maternal ferritin and serum iron and dietary heme iron intakes. Conclusions: Increased risk of GDM among women with high serum ferritin and iron levels and dietary heme iron intakes warrants further investigation.NHMR