Off-label Use of the Tandem t: slim X2™ with Control IQ® in Pregnancy: Insights from Five Case Studies.

INTRODUCTION/BACKGROUND: Hybrid closed-loop systems (HCLS), such as the Tandem t: slim X2™, are widely used in patients with type 1 diabetes mellitus (T1DM) and have well-established benefits in glycemic control. However, evidence supporting their use during pregnancy and the peripartum period remains limited. CASE PRESENTATION: We conducted a descriptive observational case series from August 2024 to February 2026 of five pregnant women with T1DM using the Tandem t: slim X2™ with Control- IQ® off-label during pregnancy, labor, and the early postpartum period. Glycemic control improved during pregnancy, with mean TIRp increasing from 50.9±17.9% before HCLS initiation to 61.0±14.4% in the third trimester, alongside a reduction in HbA1c from 7.2±1.0% to 6.0±0.5%. Preeclampsia occurred in three of the five cases. In Cases 1 to 4, HCLS remained in automated mode during labor and delivery, with Sleep Activity activated for 33%-40% of the time and latethird- trimester settings maintained. Case 5 suspended HCLS before labor and restarted two days postpartum. Mean pregnancy-specific time in range (TIRp) during labor and delivery was 64.3±10.7%, with minimal hypoglycemia (1.5±2.6%). Early postpartum period (days 1-3) mean TIR was 80.8±14.6%, and time below range (TBR) was 2.3±1.1%. Neonatal hypoglycemias were reported in three of the five cases. CONCLUSION: This case series suggests that Tandem t: slim X2™ Control-IQ® is safe and may improve glycemic control during pregnancy and the peripartum period. Further studies comparing this approach with standard care are needed to comprehensively evaluate its effects on glycemic control and maternal and neonatal outcomes.