Impact of the Menstrual Cycle on Continuous Glucose Monitoring - Derived Glycemic Parameters in Adolescent Girls With Type 1 Diabetes: A Retrospective Observational Study

Background and Objectives: Emerging clinical data indicate that glucose levels in women with type 1 diabetes (T1D) fluctuate throughout the menstrual cycle. However, data concerning the adolescent population remain sparse. This study aimed to compare continuous glucose monitoring (CGM)-derived glycemic metrics between the early follicular and late luteal phases in adolescent girls with T1D in order to establish a clinical basis for phase-specific treatment adjustments. Materials and Methods: Ninety-nine menstrual cycles from 34 female adolescents with T1D were retrospectively analyzed. Time in range (TIR), time above range (TAR), time below range (TBR), mean glucose, and glucose variability were compared between the early follicular and late luteal phases. Additional analyses were performed to evaluate the impact of different insulin delivery methods and to assess glycemic metrics across subgroups by glycemic control. Results: During the late luteal phase, TIR was significantly lower, while TAR and mean glucose were significantly higher compared to the early follicular phase (p < 0.05). Although the continuous subcutaneous insulin infusion (CSII) group achieved better overall glycemic metrics then the multiple daily injections (MDI) group, phase-related fluctuations in TIR and TAR reached significance precisely within the CSII group. Furthermore, glycemic shifts in TAR, TBR and mean glucose were especially pronounced in adolescents with tight glycemic control (HbA1c < 7.0%). Conclusions: The late luteal phase is associated with significant glycemic deterioration in adolescent girls with T1D, particularly in those with optimal glycemic control. These findings underscore the need for targeted education and menstrual-cycle-tailored insulin dose adjustments.