Guaranteeing adequate carbs before postpartum oral glucose tolerance testing may not be necessary

Postpartum patients undergoing oral glucose tolerance testing (OGTT) may not need a three-day preparatory diet of at least 150 g of carbohydrate intake beforehand, a recent study found.

Researchers analyzed data from postpartum patients in two prospective studies, the Balance after Baby Intervention (BABI) and the Study of Pregnancy Regulation of Insulin and Glucose (SPRING). Carbohydrate intake was measured with 24-hour dietary recall in SPRING and by food-frequency questionnaires over six weeks in BABI. Both studies performed two-hour 75-g OGTTs, with data from six to 24 weeks postpartum and six to nine weeks postpartum, respectively, included in the current analysis. The main outcome measure was 120-minute post-OGTT glucose level. The results were published April 25 by the Journal of Clinical Endocrinology & Metabolism.

BABI included 177 patients who had recently had gestational diabetes, and SPRING included 104 patients who had risk factors for the condition. Eighty-five percent of those in SPRING and 73% of those in BABI were breastfeeding at the time of the study visit. No relationship was seen between carbohydrate intake and 120-minute post-OGTT glucose level in either study population, and adding breastfeeding status to the model did not change the results. An inverse relationship was noted between the glycemic index of food consumed beforehand and 120-minute post OGTT glucose level in SPRING (P=0.04). In BABI, glycemic index and glycemic load were both associated with post-OGTT glucose levels (P=0.02); this relationship remained significant for glycemic index in the adjusted model (P=0.04).

The authors noted that carbohydrate intake was based on self-report and that information on glycemic index and glycemic load were only available in BABI, among other limitations. They concluded that while the American Diabetes Association recommends a preparatory diet of at least 150 g of carbohydrates for three days before diagnostic OGTT, the current analysis found no relationship between recent carbohydrate intake and OGTT glycemia in postpartum patients and indicated that diets with a low glycemic index may raise OGTT glucose levels in this group. “These data underscore the importance of developing new diagnostic methods for diabetes in pregnancy that are not susceptible to variability based on recent dietary intake,” the authors wrote. “Nevertheless, our primary analysis implies that a preparatory diet focused on carbohydrate content may not be necessary in the postpartum setting.”