Background
The “gold standard” for gestational diabetes mellitus (GDM) diagnosis, the oral glucose tolerance test (OGTT), has disadvantages including suboptimal sensitivity and specificity, and poor tolerability. However, no potential substitute tests currently have sufficient evidence for their use. Continuous glucose monitoring (CGM) potentially represents a more acceptable and comprehensive test for GDM. The aim of this study was to explore the Freestyle Libre Pro 2 as a diagnostic test for GDM, assessing its acceptability in pregnancy and correlating CGM results with OGTT results and with the risk factors of GDM.
Methods
Prospective cohort study at two Sydney metropolitan hospitals. Women wore the CGM device for 7 days at 24-28 weeks gestation, undergoing a 75-grams glucose OGTT (IADPSG criteria) on day 7. Participants then evaluated CGM/OGTT acceptability via two online surveys. CGM distribution/variability parameters and percentage of time spent in the recommended range for pregnancy (3.5-7.8), combined in the CGM Score of Variability (CGMSV) 1 were triangulated with OGTT results and GDM risk factors.
Results
Of the 107 women recruited, 87 (81%) were included in the study: 77 (88%) had negative and 10 (12%) positive OGTT (NGT, GDM). No significant difference was found in terms of demographics and CGM parameters between NGT and GDM. Although not statistically significant, CGM distribution parameters (mean, standard deviation and coefficient of variation) and variability parameters (mean amplitude of glycemic excursion and mean of daily differences) resulted higher in GDM, whereas the time spent in the range was higher in NGT. Women evaluated CGM as significantly more acceptable than OGTT (81% vs 27% 5/5 general acceptability, p<0.001).
Of the 58 NGT for which risk-factor score-OGTT-CGMSV triangulation was completed, we considered 35 were true negative (risk-factor score concordant with OGTT and CGMSV). We considered four women false negative (FN) (OGTT discordant with both risk-factor score and CGMSV). Triangulation identified one potentially false positive (FP) woman (positive OGTT but normal CGMSV and low risk-factor score).
Conclusions
CGM represented a more acceptable alternative to the OGTT for GDM diagnosis in this study. Its triangulation with GDM risk factors could allow an independent evaluation of the OGTT results. Further research on larger cohorts of patients evaluating additional triangulation elements, as GDM outcomes, is needed to confirm the results of this study and to progress the use of CGM for GDM diagnosis.