Objective: To investigate the relationship between maternal vitamin D status and glucose intolerance, and its impact on pregnant women and their newborns. Methods: A cohort of pregnant women were divided into three groups: women with gestational diabetes mellitus, ones with normal results both after the 50 gr and 100 gr OGTT (CG-1) and ones having a positive result after the 50 gr OGTT screening but negative results for gestational diabetes mellitus (GDM) after the 100 gr OGTT (CG-2) Results: The newborn length in CG-1 was greater than in GDM and CG-2 (p= 0.002 and p= 0.02). Fasting blood glucose and insulin resistance (IR) were negatively correlated with length of the newborns (r=-0.3, p=0.03 and r=-0.3, p=0.01). The newborns of women with GDM had lower APGAR-1 and 5 scores than those of CG-1 and CG-2 (APGAR-1 p= 0.001 and p= 0.004, APGAR-5 p=0.005 and p=0.007, respectively). APGAR scores were correlated negatively with IR (APGAR-1 r=-0.32, p=0.01, APGAR-5 r=-0.3, p=0.03) and positively with 25OHD levels (APGAR-1 r=0.3, p=0.01, APGAR-5 r=0.3, p=0.02). Conclusion: Vitamin D deficiency, gestational diabetes and insulin resistance are interrelated. Severe vitamin D deficiency during pregnancy is associated with poor pregnancy and neonatal outcome.