Compliance of Prenatal Patients with Dietary Instructions Prior to Blood Glucose Testing and a Comparison of Mixed Meal Screening Tests to Glucose Load Screening Tests

Three different instruction methods and their influence on selection of a breakfast test meal were studied. Subjects were 139 pregnant, Caucasian females screened for gestational diabetes by two-hour postprandial blood glucose evaluation. Macronutrient components and kilocalories of the self-selected meals were variables analyzed and compared to the nutrient pattern of a standard meal plan. The effect of varying levels of nutrients on blood glucose values was examined.

Subjects were assigned randomly to one of three groups. Subjects in Group I were given no written or verbal instructions about test meal selection but were instructed to eat breakfast. Written instructions in the form of a sample meal pattern card and foods to avoid were given to Group II and Group III subjects. Group III subjects also were given verbal explanation and amplification of the written directions. Fasting blood glucose levels were tested, subjects consumed their test meals, and a second blood sampling was performed two hours after the test meal. Subjects were asked to recall foods and beverages consumed. The entire testing process was repeated for 45 of the subjects at a later date.

Group assignment significantly (p<.01) affected kilocalorie and carbohydrate (p<.0001) levels in meals selected by subjects during the first testing process. Group I subjects selected meals significantly (p<.03) higher in kilocalories and carbohydrate than Groups II and III. Group II and Group III did not select meals that were significantly different.

When meal selections were compared to nutrient and kilocalorie levels in the standard meal plan, Group I subjects selected meals significantly higher in fat (p<.0009), carbohydrate (p<.0008), and kilocalories (p<.0001) during the first testing process. In the first test meal, Group II subjects selected meals significantly higher in fat (p<.0001), protein (p<.001), and kilocalories (p<.005) than the standard. Group III subjects selected a meal in which no nutrient components were significantly different from the standard. In the second test process, Group II subjects were the only group whose meal selections differed from the standards. Fat (p<.009) and kilocalories (p<.02) were significantly higher in the Group II meals. Carbohydrate was the only nutrient in both test meals which was positively (p<.005) correlated with blood glucose.

Differences between detection of gestational diabetes using a glucose load and one-hour blood glucose levels and/or a mixed meal and two-hour blood glucose levels were investigated. Twelve subjects had both a test meal screening and a one-hour glucose load screening. A total of 30 subjects were screened with 50 gm glucose solution and one-hour blood glucose values. These 30 subjects were compared with 45 subjects who had a second two-hour postprandial screening.

Thirty-seven percent of the 30 subjects tested with a glucose load had one-hour blood glucose values above the upper limits of normal. Only 4% of the 45 subjects tested with a mixed meal had blood glucose values above the upper limits of normal.

Of the 12 subjects tested by both methods, 50% were considered to have blood glucose levels above the upper limits of normal after a glucose dose. None of the 12 had blood glucose values above the upper limit of normal following a test meal. However, these two different tests were done at different gestational ages in the same individual subject.

In general, carbohydrate and kilocalorie content of self-selected test meals were influenced by instructional method, i.e., group assignment. Group III subjects who received the most instructions in the form of verbal and written guidelines, chose meals closest to a standard meal pattern. In this study, carbohydrate was the only nutrient which positively influenced blood glucose in both test meals. Screening tests using an oral glucose load detected a higher percentage of abnormally elevated blood glucose values than did screening with a mixed meal in this study.