An Observational Study on the Impact of Menstrual Cycle Phases on Carbohydrate Intake, Insulin Delivery and Glycaemia in Women With Type 1 Diabetes Using MiniMed 780G Automated Insulin Delivery System.

AIMS: To quantify changes in carbohydrate intake, insulin delivery and glycaemia across menstrual cycle phases in women with type 1 diabetes using the MiniMed 780G automated insulin delivery system (MM780G). MATERIALS AND METHODS: Women on MM780G provided menstrual cycle data. Continuous glucose monitoring and insulin delivery data were retrieved from the CareLink portal. Daily values for time in range (TIR, 3.9-10 mmol/L), total carbohydrates, total basal, total bolus and total insulin were calculated. Menstrual phases were classified using two methods: Method 1 compared the pre-menses week with the menses week; Method 2 compared five physiological phases with mid-follicular as reference. Linear mixed-effects models with random intercepts for participant and cycle were fitted. RESULTS: Fifteen women (mean age 35.9 years, BMI 23.3 kg/m2, HbA1c 50.8 mmol/mol [6.8%]) contributed 118 cycles. In the pre-menses week, carbohydrate intake (β = +0.164 g kg-1, adjusted p = 0.003), total daily bolus (β = +0.018 U kg-1, adjusted p = 0.001), total daily basal (β = +0.011 U kg-1, adjusted p = 0.003) and total daily dose (β = +0.029 U kg-1, adjusted p < 0.001) were significantly higher than the menses week, yet TIR was lower (β = -3.487 percentage points, adjusted p < 0.001). In Method 2, total daily basal and total daily dose were significantly higher in the late luteal phase, and TIR was lower in the mid luteal phase (β = -3.34 percentage points, adjusted p = 0.007). CONCLUSIONS: Menstrual cycle phase is associated with significant changes in carbohydrate intake, insulin delivery and TIR in women using MiniMed 780G. Despite increased insulin delivery, TIR was lower in the luteal phase, suggesting partial adaptation to menstrual cycle-related physiological changes.