TCF7L2 risk haplotype CTTC (r2 rs7901695 vs. rs4506565 = 0.96, r2 rs7901695 vs. rs7903146 = 0.88, r2 rs7901695 vs. rs12243326 = 0.55, r2 rs4506565 vs. rs7903146 = 0.92, r2 rs4506565 vs. rs12243326 = 0.58, r2 rs7903146 vs. rs12243326 = 0.60) was associated to the risk of GDM and to higher levels of fasting glycemia, 60’ and 120’ OGTT glycemia and area under the curve. The gene discussed is TCF7L2; the disease is gestational diabetes.