The standardized mean differences (SMD) in women who had GDM compared to pregnant women without were 0.25 μg/dL (95% CI: 0.001–0.50) for iron, 1.54 ng/mL (0.56–2.53) for ferritin, 1.05% (0.02 to 2.08) for transferrin saturation, and 0.81 g/dL (0.40–1.22) for hemoglobin. This evidence concerns the gene TF and gestational diabetes.