Low Glucose at 3-Hour 100 Gram Oral Glucose Tolerance Test: Implications for Glucose Control in Gestational Diabetes

Objective: To assess the clinical significance of a low 180-minute glucose value in a 100gr oral glucose tolerance test (OGTT) and a single high abnormal value. Design: A retrospective cohort study. Setting: A single outpatient health clinic. Population: Women with one abnormal high OGTT glucose value. The study group included women with 180-minute plasma glucose levels of ≤60 mg/dl and one abnormal value in the OGTT. The control group was comprised of women with one abnormal value in the OGTT and normal 180-minute glucose value. Methods: Pregnancy related outcomes and level of glycemic control of both groups were compared. Main outcome measures: The primary outcome was glycemic control, defined as fasting blood glucose measurements>90 mg/dl or post-prandial glucose values >140 mg/dl or 120 md/dl (1-hour and 2-hour post-prandial, respectively) in>30% of the measurements. Secondary outcomes were the rate of insulin treatment and the perinatal outcome consisting of birthweight, large-for-gestational-age and polyhydramnios. Results: 301 women were included, of them, 143 in the study group and 158 in the control group. Pre-pregnancy body mass index, first trimester fasting glucose levels, previous gestational diabetes mellitus, and familial diabetes were similar for both groups. Suboptimal glycemic control was more prevalent among the women in the study group (14% vs. 5.1%, respectively, P=0.01). The need for insulin treatment was similar in both groups (9.8% vs. 4.4%, P=.1). Conclusion: Women with one abnormal value and a 180-minute hypoglycemia in the OGTT are at increased risk for suboptimal glycemic control.