GSTM1 and gestational diabetes: In particular, after adjusting for confounders, Hb levels greater than 130 g/L in the first trimester significantly increased the GDM risk (OR: 1.274 for 130 g/L ≤ Hb < 150 g/L; OR: 1.844 for Hb ≥ 150 g/L), whereas a significantly decreased risk of preterm birth was observed in the women whose pre-pregnancy BMI was < 24 kg/m2 (OR: 0.768 for 130 g/L ≤ Hb < 150 g/L; OR: 0.233 for Hb ≥ 150 g/L).