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Carbohydrate Intake Before Oral Glucose Tolerance Test May Prevent Accurate Diagnosis of Gestational Diabetes

Key findings

  • Using data from an ongoing prospective study, Massachusetts General Hospital researchers evaluated how carbohydrate intake on the day preceding an oral glucose tolerance test (OGTT) affected post-load glucose levels in pregnant women
  • The 95 participants were considered at high risk of gestational diabetes mellitus (GDM)
  • At a median of 26 weeks' gestation, there was an inverse linear relationship between carbohydrate intake and 60-minute post-OGTT blood glucose level (r=-0.28; P=0.007)
  • Lower carbohydrate intake was associated with significantly higher blood glucose at 30 (adjusted ß=-6.5 mg/dl, P<0.01), 60 (adjusted ß=-8.9 mg/dl, P<0.01), and 120 minutes (adjusted ß=-8.1 mg/dl, P=0.01) post-OGTT and with higher glucose area under the curve (adjusted ß=-767; P<0.01)
  • For accurate diagnosis of GDM, medical societies may need to recommend a standardized preparatory diet for pregnant women to follow before an OGTT, but more research is needed before current guidelines are changed

In 2007, the Fifth International Workshop–Conference on Gestational Diabetes Mellitus (GDM) concluded that pregnant women should consume a moderate- to high-carbohydrate diet for three days prior to an oral glucose tolerance test (OGTT). Current U.S. medical society guidelines do not advise a preparatory diet, but some clinicians recommend it to pregnant patients.

Now, Camille E. Powe, MD, endocrinologist and co-director of the Diabetes in Pregnancy Program at Massachusetts General Hospital, Emily A. Rosenberg, MD, endocrinologist at Brigham and Women's Hospital, and colleagues have found using prospective data that carbohydrate intake on the day before an OGTT among pregnant women with risk factors for GDM does seem capable of influencing whether GDM is diagnosed. They present the details in Diabetes Research and Clinical Practice.

Study Methods

The Study of Pregnancy Regulation of INsulin and Glucose (SPRING) is a longitudinal prospective study examining insulin physiology and glucose metabolism in pregnant women at high risk of GDM. The researchers analyzed data on 95 pregnant women (24–32 weeks' gestation).

At the study visit (median 26 weeks' gestation) the participants underwent a standardized 2-hour, 75 g OGTT. They were asked to fast for at least eight hours but received no other instructions about diet or physical activity.

At the time of the OGTT, the participants completed the Automated Self-Administered 24-Hour Dietary Assessment Tool.

Primary Outcome

  • There was an inverse linear relationship between carbohydrate intake and 60-minute post-OGTT blood glucose level, the prespecified primary outcome measure (r=−0.28; P=0.007)
  • In a fully adjusted model, there was an 8.90 mg/dL increase in the 60-minute glucose level for every 50 g reduction in carbohydrate intake (P<0.01)

Secondary Outcomes

Lower carbohydrate intake was associated with:

  • Higher 30-minute glucose level (adjusted β=−6.5 mg/dL; P<0.01)
  • Higher 120-minute glucose level (adjusted β=−8.0 mg/dL; P=0.01)
  • Higher glucose AUC (adjusted β=−767; P<0.01)

Exploratory Outcome

Higher carbohydrate intake was not significantly associated with lower odds of GDM diagnosis.

Continued Scrutiny Needed

These results suggest both excessive and restrictive carbohydrate intake on the day prior to an OGTT could alter the post-load glucose levels and affect whether GDM is diagnosed. Thus, recommendations about a standardized preparatory diet may need to be added to guidelines.

However, more research is needed before current guidelines are changed. It remains to be determined how carbohydrate intake during pregnancy affects perinatal outcomes, and larger cohorts and alternatives to the OGTT should be studied.

Learn more about the Maternal-Fetal Medicine Program

Learn more about the Diabetes in Pregnancy Program

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