Quantitation of insulin sensitivity (S,) with the insulin suppression test, glucose clamp, or the minimal model method has been achieved in various clinical circumstances. The application of these techniques to pregnancy has been limited. It is important to utilize sensitive and reproducible methods to study S, changes in pregnancy to fully understand the normal and pathological metabolic alterations that occur during gestation. These techniques demonstrate that various factors (obesity, body fat distribution, age, dietary manipulation, and exercise) may affect S, measures. The various pregnancy hormones have differential effects on insulin action. There is consensus among the limited in vivo studies in human pregnancy that late gestation is associated with significantly impaired S, compared with the nonpregnant state. Studies with appropriate matching between control and gestational diabetic subjects have failed to demonstrate a significant difference in S, between groups in the third trimester.

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