RBP4 and obesity due to melanocortin 4 receptor deficiency: We propose 3 hypotheses regarding the positive statistical association between RBP4 levels and GDM risk: (1) GDM pathophysiology is related to obesity but not RBP4 levels, and serum RBP4 levels are elevated because of the increased size of adipocytes [7]; (2) RBP4 is a pathophysiological link between obesity and insulin resistance; (3) RBP4 is a modest independent risk factor for GDM (i.e., nonobese patients with GDM might express RBP4 at abnormal levels).