Hemoglobin concentration and iron supplement during pregnancy were associated with an increased risk of gestational diabetes mellitus

BACKGROUND Hemoglobin (Hb) measurement is a conventional test during perinatal visit. Hb concentration is related to iron supplement. However, studies focusing on Hb levels, iron supplement and pregnancy outcomes are scarce. This study aimed to determine whether Hb levels and iron supplement were associated with the risk of gestational diabetes mellitus (GDM). METHODS A running hospital based cohort was conducted from August, 2011. The demographic data and medical information were collected individually through questionnaires and patient medical records. Multiple linear regression was applied for the association between Hb levels, iron supplement and blood glucose. Multiple logistic regression was used for evaluating odds ratios between Hb levels, iron supplement and GDM. RESULTS Hb levels during first (T1) and second trimester (T2) of pregnancy were significantly and positively associated with blood glucose and GDM risk. After adjusting for age, pre-pregnancy BMI and other risk factors, pregnant women with Hb≥11g/dL and iron supplement had higher postprandial blood glucose at 1 hour (Hb ≥11g/dL in T2 and iron supplement in T1: β=0.860，P = <0.001; Hb ≥11g/dL in T2 and iron supplement in T2: β=0.960，P <0.001; Hb ≥11g/dL in T1 and iron supplement in T2: β=1.133, P =0.033) and GDM risks (OR=1.53, 95%CI: 1.05-2.24; OR=1.92, 95%CI: 1.13-3.35; OR=2.15, 95%CI: 1.07-4.34, respectively), compared with those with Hb<11g/dL and without iron supplement. CONCLUSION High Hb concentration and iron supplements without anemia increased postprandial blood glucose and risks for GDM. It indicates that pregnant women with good Hb levels should not be advised iron supplements during pregnancy.