Glycemic control may vary across menstrual cycle phases in women with type 1 diabetes mellitus (T1DM) using automated insulin delivery systems. An observational cohort analysis published in Diabetes, Obesity and Metabolism evaluated continuous glucose monitoring (CGM) and insulin delivery patterns across menstrual phases in women with T1DM.

The study included 48 menstrual cycles from 17 women with T1DM (mean age 39.9 ± 6.3 years; diabetes duration 30.1 ± 9.7 years; body mass index [BMI] 25.7 ± 3.6 kg/m²). Glycemic and insulin delivery metrics were compared between the late luteal phase (LLP; days −7 to −1) and early follicular phase (EFP; days 1-7) across up to three cycles per participant.

During the LLP, time in range (TIR) was lower compared with the EFP (80.7% vs. 82.7%, p < 0.05). Time above range (TAR) was higher (17.3% vs. 14.6%, p < 0.01), and mean glucose was higher (141 vs. 135 mg/dL, p < 0.01). In contrast, time below range (TBR) was higher during the EFP (2.8% vs. 2.0%, p < 0.01).

Total daily insulin dose (TDD) was elevated during the LLP (33.1 vs. 32.0 units, p < 0.05) primarily because of higher prandial insulin (19.5 vs. 18.6 units), while basal and autocorrection doses did not differ. These findings show phase-specific differences in glycemic patterns and insulin requirements, with higher glucose levels and insulin needs during the late luteal phase and greater hypoglycemia exposure during the early follicular phase.