1066-OR: Menstrual Cycle–Related Insulin Requirement Changes Are Independent of Menstrual Symptoms and PMDD in Women with Type 1 Diabetes Using an AHCL System

Introduction and Objective: Insulin sensitivity fluctuates across the menstrual cycle in type 1 diabetes (T1D). Advanced hybrid closed-loop (AHCL) systems enable real-world quantification of phase-related changes in insulin delivery and CGM metrics. We examined whether menstrual symptoms (mMDQ) or premenstrual dysphoric disorder (PMDD), and carbohydrate intake, contribute to these phase-dependent changes. Methods: Fifteen premenopausal women with T1D using MiniMed 780G (no hormonal therapy) were analyzed. Days with SmartGuard ≥70% were included; cycles with ≥2 eligible days in follicular (d1-7) and luteal (d-7 to -1) phases were analyzed. Linear mixed-effects models compared phases; Spearman tested associations of mMDQ/PMDD with phase-related changes. Results: Eighty cycles (1-10/participant) were analyzed. Luteal vs follicular phase: total daily insulin 49.2±3.7 vs 45.1±3.7 U/day; basal 18.0±1.3 vs 17.0±1.3 U/day; carbohydrate intake 197.9±18.2 vs 186.1±18.2 g/day; TIR 70.0±3.2% vs 72.9±3.2%, with higher TAR. After adjusting for carbohydrate intake, higher total daily insulin, basal insulin, total bolus and auto-correction bolus insulin, and TAR remained significant, whereas meal bolus was no longer different. mMDQ and PMDD scores were not associated with phase-related changes in insulin metrics or carbohydrate intake. Conclusion: In women with T1D using AHCL, insulin needs rise and glycemia modestly worsens in the luteal phase independent of carbohydrate intake, menstrual symptoms, and PMDD severity, suggesting physiological luteal-phase insulin resistance not fully compensated by current algorithms. Disclosure E. Takagi: None. H. Kaga: None. R. Mori: None. S. Fujikawa: None. T. Kogai: None. J. Sato: None. F. Ikeda: None. Y. Tamura: Speaker's Bureau; Current; Ono Pharmaceutical Co., Ltd., Sumitomo Dainippon Pharma Co., Ltd., Kowa Research Institute, Inc. Research Support; Ended; Kowa Research Institute, Inc. H. Watada: Research Support; Current; Sumitomo Pharma Co. Ltd., Sanwa Kagaku Kenkyusho, Kowa Company, Ltd., Taiho Pharmaceutical Co. Ltd., SBI pharma, Boehringer Ingelheim International GmbH. Speaker's Bureau; Current; Novo Nordisk, Boehringer Ingelheim International GmbH, Sumitomo Pharma Co. Ltd., Lilly, Roche Diagnostics, Merck Sharp & Dohme Corp., Daiichi Sankyo, Kyowa Kirin Co., Ltd., Bayer AG, Abbott Japan Co., Ltd., Mitsubishi Tanabe Pharma Corporation, Teijin Pharma Limited, GlaxoSmithKline plc., Sanofi K.K., embecta.