Insulin binding in human pregnancy: comparisons to the postpartum, luteal, and follicular states.

We have studied insulin binding to isolated erythrocytes from 28 nondiabetic, pregnant women and have compared these results to similar data obtained in nonpregnant, nondiabetic women. In the nonpregnant subjects insulin binding was 35% higher during the follicular stage of the menstrual cycle as compared to the luteal phase. In the pregnant women insulin binding was comparable to that seen in the nonpregnant women during the follicular phase but was higher than that seen during the luteal phase of the menstrual cycle. Insulin binding was measured in 5 pregnant women during the third trimester and in the postpartum period. In these subjects insulin binding to erythrocytes declined by 31% after delivery. These results demonstrate that erythrocyte insulin receptors are not decreased in normal human pregnancy despite the presence of hyperinsulinemia and insulin resistance. Providing erythrocyte insulin receptors are reflective of insulin receptors in other tissues in human pregnancy, these findings suggest that some factor exists in pregnancy that modulates insulin receptors in a positive manner and are consistent with the possibility that the insulin resistance in pregnancy is related to a postreceptor abnormality.