As shown in Fig. 3C, after adjusting for age and pre-pregnancy BMI, the OR of risk for GDM development increased in a stepwise manner from women with Hb ≤ 122 g/L and Hp1 allele to women with Hb > 122 g/L and Hp2-2 genotype (OR = 1.034, 95% CI: 0.274–1.469, P = 0.288; OR = 1.472, 95% CI: 0.795–2.727, P = 0.219; OR = 4.355, 95% CI: 2.437–7.784, P < 0.001; respectively). The gene discussed is GSTM1; the disease is gestational diabetes.