Relationship between ABO blood group and gestational diabetes mellitus. 
Objective: To investigate the association between the ABO blood group and gestational diabetes mellitus (GDM).  Methods: A case-control study was conducted in 600 pregnant women who received GDM screening with 50-g GCT and diagnosis by 100-g OGTT according to institutional guidelines.  The cases included 200 women with GDM and another 400 normal pregnant women were randomly selected as controls.  Various characteristics and ABO blood group were extracted from medical records and compared between cases and controls to determine their association with GDM.  Logistic regression analysis was performed to determine independent associated factors for GDM adjusting for potential confounders.  Results: Univariate analysis showed that significant factors associated with GDM were age ≥30 years, family history of DM, overweight, and obesity.  Only blood group O significantly increased risk of GDM (OR 1.51, 95% CI 1.06-2.13, p = .020).  Logistic regression analysis showed that blood group O independently increased the risk of GDM (adjusted OR 1.99, 95% CI 1.32-3.0, p = .001).  The risk of GDM was enhanced in women with blood group O with family history of DM (adjusted OR 3.5, 95% CI 1.57-7.81, p = .002) while it was attenuated among those without (adjusted OR 1.6, 95% CI 0.97-2.64, p = .064).  Conclusion: Blood group O independently increased the risk of GDM.