Continuous Glucose Monitoring-Measured Glucose Levels During Oral Glucose Tolerance Testing in Pregnancy

Background: To diagnose gestational diabetes mellitus (GDM), clinicians typically rely on the oral glucose tolerance test (OGTT). Continuous glucose monitoring (CGM) is a tool that could possibly be used to complement or replace the OGTT. Our aim is to describe CGM-derived glycemic patterns observed concurrently during the administration of a diagnostic OGTT in pregnancy. Methods: In total, 119 pregnant females underwent OGTT testing while wearing a blinded CGM sensor. Blood glucose (BG) measurements collected during the OGTT were compared with CGM-measured glucose values obtained using a Dexcom G6 Pro sensor to determine the differences between CGM-measured and BG levels during the OGTT, measure glycemic excursion during the OGTT, and determine differences in GDM diagnosis using standard BG draws during OGTT versus CGM-measured glucose levels. Results: CGM-measured glucose levels were on average higher than paired BG levels during the OGTT at each timed measurement (fasting, 1-, 2- and 3-h); fasting CGM-measured glucose levels in particular were higher than fasting BG levels by 6 ± 13 mg/dL. The median CGM minus BG-measured glycemic excursion during the OGTT was 12 and 4 mg/dL for the 75 g and 100 g OGTT, respectively. Of 28 participants diagnosed with GDM based on OGTT BG levels, 24 (86%) participants would have been diagnosed as GDM using CGM with BG-based thresholds; of 91 participants not diagnosed with GDM, 54 (59%) would also have not been diagnosed with GDM using CGM. Conclusions: CGM glucose measurements using Dexcom G6 Pro tended to be slightly higher than BG values during an OGTT, leading to more participants who would have been diagnosed with GDM if the BG-based OGTT thresholds were applied to these CGM-measured glucose values. When CGM is used for GDM diagnosis, diagnostic glucose criteria may need to be specific for the type of sensor used accounting for any bias in glucose measurement.