Timing of continuous glucose monitoring initiation and long-term glycemic trajectories in pediatric type 1 diabetes

Purpose: The long-term impact of continuous glucose monitoring (CGM) initiation on glycemic trajectories in children and adolescents with type 1 diabetes (T1D) remains unclear. We assessed 5-year glycated hemoglobin (HbA1c) trajectories according to CGM initiation timing in Korean children and adolescents with T1D. Methods: We retrospectively analyzed patients diagnosed with T1D at ≤18 years between 2015 and 2024 at a single pediatric diabetes center. Patients were categorized by CGM initiation timing (<1 month, 1-<12 months, ≥12 months, or no-CGM use). HbA1c was assessed at prespecified intervals up to 60 months, and adjusted trajectories and rates of change were estimated with linear mixed-effects models accounting for repeated measurements within patients. Results: Among 216 patients (mean follow-up, 61.3 ± 34.8 months), 69.9% used CGM and 40.7% initiated within 1 month of diagnosis. Baseline HbA1c was higher in the early-CGM group than in the delayed/no-CGM group (12.5% [IQR, 11.0-13.9] vs 11.1% [IQR, 8.8-13.2]; p<0.001), but converged within 12 months. Median HbA1c at 60 months was 6.8%, 6.8%, 7.7%, and 7.3% in the <1-month, 1-<12-month, ≥12-month, and no-CGM groups; the proportion achieving HbA1c <7.0% fell from 86.4% at 9 months to 47.1% at 60 months in the no-CGM group, which alone showed a rising trajectory in mixed-effects models (+0.27% per year; p<0.001). Conclusion: Early CGM initiation after T1D diagnosis was associated with more favorable 5-year HbA1c trajectories compared with delayed initiation or no CGM use, supporting routine early CGM adoption in pediatric T1D management.