Differences in Postload Plasma Glucose Levels between 100-g and 75-g Oral Glucose Tolerance Tests in Normal Pregnant Women: A Potential Role of Early Insulin Secretion

Objective: To demonstrate a role of early insulin secretion on plasma glucose levels after different amounts of oral glucose loads in pregnant women. Material and Method: Forty-one pregnant women with normal glucose tolerance according to the Carpenter and Coustan ’ s criteria and 25 non-pregnant women (control group) with normal glucose tolerance according to the World Health Organization criteria were enrolled. Each subject was randomly scheduled to perform both the 100-g and 75-g OGTT within a 1-week interval. Venous blood was drawn at fasting, 30-, 60-, 120-, and 180-minute intervals during both tests for determination of plasma glucose and serum insulin levels. Results: The mean (+ SE) ages of the pregnant and control groups were 33.3 + 0.9 and 31.8 + 1.4 years, respectively. The mean gestational age at the time of performing OGTT of the pregnant group was 28.7 + 0.6 weeks. In the non-pregnant group, the plasma glucose concentrations were not different between 75-g and 100-g OGTT whereas the serum insulin levels at the 30 and 180 minutes of the 100-g OGTT were significantly higher than those of the 75-g OGTT. In the pregnant group, both plasma glucose and serum insulin concentra-tions at the 120 and 180 minutes of the 100-g OGTT were significantly higher than those of the 75-g OGTT. Conclusion: The limited ability of early insulin secretion to increase when glucose load increased in the pregnant women could explain the high plasma glucose levels at 2 and 3 hours of 100-g OGTT compared t