highly significantP = 0.00
Overall, pooled meta-analysis also showed that pregnant women associated with GDM have lower level of vitamin D when compared with normal pregnant women considering the fixed-effects model (OR = −0.18, 95% CI − 0.22 to − 0.14; P = 0.00) with highly significant heterogeneity (I 2 = 90.95%; P = 0.00) that demonstrates that deficient level of vitamin D is associated with an increased risk of GDM.