Ryan et al. studied 14 women, who had a history of GDM and did not have signs of either diabetes or impaired glucose tolerance after birth, but in all of them serum glucose levels after oral glucose tolerance tests were significantly enhanced compared to the control group, which they attributed to a defect of insulin secretion.20 Also others described, that women with normal glucose tolerance and a history of gestational diabetes had significant impairments of beta-cell function at normal insulin sensitivity after birth.21 This evidence concerns the gene INS and diabetes mellitus.