The association of iron status, supplement iron in the first‐trimester pregnancy with gestational diabetes mellitus: A nested case–control study

Abstract Aims The objective of this study was to examine whether the level of iron and iron supplements in the first‐trimester pregnancy is associated with gestational diabetes mellitus (GDM). Methods This was a nested case–control study using data from an established cohort in the Hunan Provincial Maternal and Child Health Hospital (HPMCHH) in South China. A total of 119 patients with GDM and 238 controls were enrolled in the study. Iron status indicators were tested in early pregnancy. Information on iron supplements use was collected by questionnaires. Binary logistic regression was used to obtain odds ratio (OR). The relative excess risk of interaction (RERI) was applied to evaluate the interaction. Results We observed that pregnant women with normal ferritin levels (≥30 ng/ml) and iron supplements were associated with a 3.701‐fold increased risk of GDM (OR: 3.701, 95% CI: 1.689–8.112) compared with the ferritin <30 ng/ml and without iron supplements group. Similarly, pregnant women with normal serum iron (SI) levels (≥9 μmol/L) and iron supplements were associated with a 5.447‐fold increased risk of GDM (OR: 5.447, 95% CI: 2.246–13.209) compared with the SI < 9 μmol/L and without iron supplement group. We found an additive interaction between ferritin and iron supplements on the presence of GDM (RERI: 1.164, 95%CI: 0.333–1.994) and SI and iron supplements on the risk of GDM (RERI: 6.375, 95%CI: 4.494–8.256). Conclusion Pregnant women with normal ferritin or SI levels and iron supplements could significantly increase the risks for GDM.