Effects of pregnancy on hemoglobin AIc in normal, gestational diabetic, and diabetic women

Hemoglobin AIc, a normal minor hemoglobin, has glucose linked by a Schiff base to the N terminal end of the beta chain. The glucose interferes with the binding of 2,3 diphosphoglycerate, probably resulting in an increased affinity of that hemoglobin for oxygen. Hb AIc is increased to twice normal levels in juvenile onset (insulin dependent) diabetes. In the present studies, the Hb AIc, when expressed as per cent of total hemoglobin, was found to be elevated slightly in pregnant normal (m=6.97 %), pregnant nondiabetic obese (m=6.89 %), and gestationally diabetic subjects (m=8.77 %) above that of normal females (m=5.68 %). A remarkable difference was observed between the nonpregnant diabetics (m=12.77 %) and the pregnant diabetics (m=8.46 %). This decrease in the level of Hb AIc in diabetics who are pregnant more than 30 wk may reflect either a better state of diabetic control and/or a compensatory mechanism to protect the fetus by facilitating oxygen exchange from mother to fetus.