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
Karanrat Soonthornpun MD*, Supamai Soonthornpun MD**, Atchara Thamprasit BN**, Jiraporn Aksonteing BN***
Affiliation : * Department of Obstetrics and Gynaecology, Faculty of Medicine, Prince of Songkla University, Hat Yai, Songkhla ** Department of Medicine, Faculty of Medicine, Prince of Songkla University, Hat Yai, Songkhla *** Department of Nursing, Songklanagarind Hospital, Faculty of Medicine, Prince of Songkla University, Hat Yai, Songkhla
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 to
those of 75-g OGTT.
Keywords : Oral glucose tolerance test, Normal pregnant women, Plasma glucose, Insulin secretion
