BACKGROUND AND PURPOSE:

• There is some evidence to suggest that the time between last meal and the 1-hour oral glucose tolerance test (OGTT) may impact the probability of a positive screening result
• Sperling et al. (Obstetrics & Gynecology, 2022) evaluate the effect of fasting prior to the 1-hour OGTT on gestational diabetes mellitus (GDM) screening results

METHODS:

• Single-center, prospective randomized trial
• Participants
  • Pregnant patients without pregestational diabetes
• Interventions
  • Fasting: Fasting for ≥6 hours prior to testing
  • Fed: Oral intake within 2 hours of the 50-g, 1-h OGTT
• Study design
  • The 1-h OGTT was administered >24 weeks
  • Positive screen result: Defined as a serum glucose level of ≥140 mg/dL
  • Protocol adherence was assessed by a survey administered immediately after the OGTT
  • Planned enrollment of 100 participants in each group to detect absolute difference of ≥20 percentage points on screen-positive rate | Assuming two-sided α=0.05 and power=0.8
• Primary outcome
  • 1-h OGTT screen-positive rate
• Secondary outcomes
  • Mean 1-h OGTT glucose values
  • GDM diagnosis
  • Maternal and neonatal outcomes
  • Patient perception of the test

RESULTS:

• Fasting: 97 participants | Fed: 98 participants
  • Adherence to fasting: 97.9% | Adherence to fed: 91.8%
• The screen-positive rate was significantly higher in the fasting than the fed group
  • Fasting: 32.0%
  • Fed: 13.3%
  • P=0.002
• The mean glucose value was also higher in the fasting group
  • Fasting: 127.7 mg/dL
  • Fed: 113.3 mg/dL
  • P=0.002
• The incidence of GDM in the fasting group was non-significantly higher than the fed group
  • Fasting: 12.4%
  • Fed: 5.1%
  • P=0.08
• Patients were asked if given a choice between fasting or eating prior to screening
  • Preference to eat: 71.1%
  • Preference to fast: 28.9%
• There were no significant differences in maternal or neonatal outcomes

CONCLUSION:

• Fasting for 6 hours prior to 1-hour OGTT administration had higher screen-positive rates and greater mean glucose levels than those who ate within 2 hours of test administration
• The authors state

…previous studies have demonstrated an increase in glucagon production and a marked delay in insulin concentration followed by a large release of insulin after a prolonged fast that eventually returns to a normal metabolic state after a period of refeeding in individuals without diabetes and those with prediabetes 

Learn More – Primary Sources:

Fasting Compared With Fed and Oral Intake Before the 1-Hour Oral Glucose Tolerance Test

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