Fasting Compared With Fed and Oral Intake Before the 1-Hour Oral Glucose Tolerance Test: A Randomized Controlled...

To evaluate the effect of fasting compared with eating before the 1-hour oral glucose tolerance test (OGTT) on gestational diabetes mellitus (GDM) screening results.

In a single-center, prospective randomized trial, participants were randomized to: 1) fasting for 6 or more hours or 2) oral intake ("fed") within 2 hours of the 50-g, 1-hour OGTT. The 1-hour OGTT was administered after 24 weeks of gestation. A positive screen result was defined as a serum glucose level of 140 mg/dL or higher. Protocol adherence was assessed by a survey administered immediately after the OGTT. We planned to enroll 100 participants in each group to detect an absolute difference of 20 percentage points or more on the 1-hour OGTT screen-positive rate using Fisher exact test, assuming an estimated screen-positive rate of 45% in the fasting and 25% in the fed group and 10% attrition, with a two-sided α=0.05, power=0.8. The primary outcome was the 1-hour OGTT screen-positive rate. Secondary outcomes included mean 1-hour OGTT glucose values, GDM diagnosis, maternal and neonatal outcomes, and patient perceptions regarding the 1-hour OGTT.

From November 2020 through April 2021, 200 participants were randomized. One hundred ninety-five completed the 1-hour OGTT (97 fasting, 98 fed). Participant surveys confirmed 97.9% (n=95) adherence to the fasting and 91.8% (n=90) adherence to the fed groups. The screen-positive rate was significantly higher in the fasting than the fed group (32.0% vs 13.3%, respectively, P=.002), as was the mean glucose value (127.7 mg/dL vs 113.3 mg/dL, P=.002). The incidence of GDM in the fasting group was 12.4% (n=12) and in the fed group was 5.1% (n=5) (P=.08). There were no significant differences in maternal or neonatal outcomes.

Fasting for 6 or more hours doubled the incidence of a positive 1-hour OGTT result when compared with eating within 2 hours of the test.

ClinicalTrials.gov, NCT04547023.