MTHFR and gestational diabetes: The pooled results demonstrated that the MTHFR gene C677T polymorphism was significantly related to the risk of GDM in the allele model (OR=1.59, 95%:1.05-2.41, P=0.03; I2 = 94%, P<0.001) (Figure 2), homozygote model (OR=2.24, 95%:1.44-3.50, P<0.001; I2 = 89%, P<0.001) (Figure 3), heterozygote model (OR=1.28, 95%:0.99-1.65, P=0.05; I2 = 82%, P<0.001) (Figure 4), dominant model (OR=1.55, 95%:1.16-2.06, P=0.003; I2 = 89%, P<0.001) (Figure 5) and recessive model (OR=1.89, 95%:1.32-2.72, P<0.001; I2 = 86%, P<0.001) (Figure 6).