Association between time in range and adverse pregnancy outcomes in patients with gestational diabetes mellitus

Introduction. Gestational diabetes mellitus (GDM) is associated with an increased risk of adverse obstetric and perinatal outcomes. Self-monitoring of blood glucose using a glucometer reflects only individual measurements and may fail to detect short-term episodes of hyperglycemia and asymptomatic hypoglycemia. Continuous glucose monitoring (CGM) allows the glycemic profile to be assessed over time using integrated metrics, including time in range (TIR). However, the optimal target TIR values for pregnant women with GDM and their association with pregnancy outcomes remain insufficiently studied.
Objective: to assess the impact of achieving the recommended glycemic ranges according to CGM data on adverse pregnancy outcomes in patients with GDM.
Material and methods. A retrospective cohort study was conducted in 100 patients with GDM who were followed up at medical centers of the Sverdlovsk Region and used the FreeStyle Libre 2 CGM system during pregnancy. CGM metrics were calculated over two-week intervals (from 3 to 13 intervals, December 2024 — November 2025) from sensor placement to delivery. Time in range (TIR), time above range (TAR), and time below range (TBR) were assessed. Glucose ranges of 3.5-7.8 and 3.5-7.0 mmol/L were chosen as targets. Patients were divided into groups according to the presence of the studied pregnancy outcomes: preterm birth (<37 weeks), cesarean section (CS), birth trauma, the need for neonatal respiratory support, including Continuous Positive Airway Pressure (CPAP) devices or mechanical ventilation (MV), neonatal admission to the intensive care unit (ICU) or the neonatal intensive care unit (NICU), and neonatal hypoglycemia (<2.6 mmol/L). The Student’s t-test was used to compare the mean values of CGM metrics (p<0.05).
Results. Although TIR was relatively high: 95.1±4.9% (3.5-7.8) and 90.2±7.5% (3.5-7.0); TBR was 1.4±2.0%. No statistically significant differences in TIR and TAR were found between the groups with and without the studied outcomes (p>0.05). In the preterm birth group, a trend toward higher TBR was noted (2.7±5.2% versus 1.3±1.5%), which did not reach significance (p=0.071).
Conclusion. In patients with gestational diabetes mellitus using the FreeStyle Libre 2 continuous glucose monitoring system, high time-in-range values and a low proportion of time below range were observed. No statistically significant associations were found between time in range or time above range and adverse obstetric or neonatal outcomes. However, a trend toward increased time below range was observed in patients with preterm birth, indicating the need for further investigation of the potential role of hypoglycemia in adverse pregnancy outcomes in larger cohorts.

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