Bihormonal dysregulation of insulin and glucagon contributes to glucose intolerance development at one year post-delivery in women with gestational diabetes: a prospective cohort study using an early postpartum 75-g glucose tolerance test.

Gestational diabetes mellitus (GDM) is known to be a significant risk factor for the future development of type 2 diabetes. Here, we investigated whether a precise evaluation of β- and α-cell functions helps to identify women at high risk of developing glucose intolerance after GDM. Fifty-six women with GDM underwent a 75-g oral glucose tolerance test (OGTT) at early (6-12 weeks) postpartum. We measured their concentrations of glucose, insulin, proinsulin and glucagon at fasting and 30, 60 and 120 min. At 1-year post-delivery, we classified the women into a normal glucose tolerance (NGT) group or an impaired glucose tolerance (IGT)/diabetes mellitus (DM) group. Forty-three of the 56 women completed the study. At 1-year post-delivery, 17 women had developed IGT/DM and 26 women showed NGT. In the early-postpartum OGTTs, the IGT/DM group showed a lower insulinogenic index, a less glucagon suppression evaluated by the change from fasting to 30 min (ΔGlucagon 30 min), and a higher glucagon-to-insulin ratio at 30 min compared to the NGT group. There were no significant between-group differences in proinsulin levels or proinsulin-to-insulin ratios. Insulinogenic index <0.6 and ΔGlucagon 30 min >0 pg/mL were identified as predictors for the development of IGT/DM after GDM, independent of age, body mass index, and lactation intensity. These results suggest that the bihormonal disorder of insulin and glucagon causes the postpartum development of glucose intolerance. The measurement of plasma insulin and glucagon during the initial OGTT at early postpartum period can help to make optimal decisions regarding the postpartum management of women with GDM.