CGM Metrics and the Risk of Pregnancy Complications in Type 1 Diabetes: A Secondary Exploratory Analysis of the CRISTAL Trial

OBJECTIVE: To examine the associations between continuous glucose monitoring (CGM) metrics, including glucose management indicator (GMI) and overnight glucose levels, and pregnancy outcomes in women with type 1 diabetes. RESEARCH DESIGN AND METHODS: Secondary exploratory analysis of the CRISTAL trial including 95 pregnant women with type 1 diabetes using CGM. Associations were assessed using logistic regression and Spearman correlations, presented as odds ratios (95% confidence intervals [CIs]) adjusted for baseline HbA1c. GMI validity was assessed using scatter and Bland-Altman plots. RESULTS: Each 5% increase in overall pregnancy-specific time-in-range (TIRp) decreased the odds of gestational hypertension (odds ratio [OR] 0.63, 95% CI 0.41-0.97), birthweight >4.5 kg (OR 0.56, 95% CI 0.32-0.96), and neonatal hypoglycemia requiring hospital care (OR 0.09, 95% CI 0.01-0.57). Each 5% increase in overnight TIRp decreased the odds of gestational hypertension (OR 0.71, 95% CI 0.52-0.98) and neonatal hypoglycemia requiring hospital care (OR 0.15, 95% CI 0.03-0.79). Each 5% increase in overall time-above-range (TARp) increased the odds of birthweight >4.5 kg (OR 1.76, 95% CI 1.05-2.96), respiratory distress (OR 1.55, 95% CI 1.02-2.37), and neonatal hypoglycemia requiring hospital care (OR 5.10, 95% CI 1.14-22.78). Each 5% increase in TARp overnight increased the odds of hospital care for neonatal hypoglycemia (OR 2.55, 95% CI 1.15-5.66). Each 0.28 mmol/L increase in mean glucose and 0.5% increase in GMI were associated with increased respiratory distress (OR 1.54, 95% CI 1.07-2.23 and OR 6.15, 95% CI 1.33-28.40). Every 0.28 mmol/L increase in glycemic variability (SD) was associated with gestational hypertension (OR 1.69, 95% CI 1.02-2.80) and birthweight >4.5 kg (OR 2.31, 95% CI 1.20-4.43). Several combinations of CGM metrics (TIRp[-night], TARp[-night], SD, mean glucose) improved discriminative performance for pregnancy outcomes. GMI and HbA1c values were discordant. CONCLUSIONS: Specific combinations of CGM metrics, including overnight TIRp/TARp, may be informative for predicting pregnancy outcomes. GMI and HbA1c should not be considered interchangeable for glycemic control during pregnancy.