Following adjustment for maternal age, race, family history of type II diabetes mellitus and prepregnancy BMI, patients with HO-1 levels ≥3.05 ng/ml (highest decile) experienced a 74% reduction in GDM risk (95% CI, 0.09–0.77) compared with patients whose HO-1 concentrations were <1.23 ng/ml. The gene discussed is HMOX1; the disease is type 2 diabetes mellitus.