INTRODUCTION
The size and duration of glucose fluctuations throughout the day govern the overall daily glycaemic control. This is particularly significant during pregnancy in which physiological changes promote diabetogenesis. Furthermore maternal normoglycaemia is associated with lower risk for complications in patients with Type 1 Diabetes (T1D)1-4 ,Type 2 Diabetes (T2D) 1, 4,5. Pregnant women with gestational diabetes (GDM) have been shown to have greater blood glucose fluctuations with higher mean and standard deviations in glucose levels6-8 and a greater mean amplitude of glycaemic excursion (MAGE)6, 8 compared to pregnant women without GDM (non-diabetic pregnancies)9.
Continuous glucose monitoring (CGM) is a way of objectively, accurately, and painlessly measuring these blood glucose variations5, 9, 10. Previous studies on CGM use in pregnancy were based on earlier versions of CGM sensors that required calibration1, masked the glucose readings 2, 3and only had a sensor-life of 3 2, 3 to 6 days1, 4. In September 2016, the U.S. Food and Drug Administration (FDA) approved the Freestyle Libre Pro Glucose Monitoring System, a calibration free-continuous glucose monitoring (CF-CGM) system for blinded professional use in clinics, and in September 2017, the Freestyle Libre for unblinded personal use by patients became available. These sensors are factory calibrated and require no participant or healthcare professional involvement. Both systems have a disposable sensor which is applied to the back of a patient’s arm and can be worn for up to 14 days ensuring adequate data is available for clinical evaluation 11. With the Freestyle Libre Pro, a handheld device is used to download the blood glucose information stored in the sensor at the end of the 14-day wear, but the glucose data is not visible during the time of application. Patients using the Freestyle Libre can receive CGM feedback any time by intermittently scanning the sensor. 12.
Evidence in the form of randomized-controlled trials (RCTs) and cohort studies suggests that the control of glycaemic variability, characterized by glucose excursions and fluctuations can be better managed with CGM feedback during pregnancy 13-16. Being able to rapidly identify the consequences on blood glucose level of factors such as diet and exercise and make behavioural changes accordingly has been found to improve maternal glycaemic control. Moreover, it has led to better obstetric and neonatal outcomes, in studies involving pregnant women with T1D16, T2D13 and gestational diabetes9, 14. The ease of interpretation the glucose readings from CGM feedback can empower, and serve as an educational tool for patients to better manage their glucose levels during pregnancy 5, 9, 15. However all the randomised trials to date have been conducted in diabetic patients13, 14, 16 who are already highly motivated to improve their glycaemic control and no studies have been conducted in healthy non-diabetic pregnant women.
To our knowledge, our study is the first to evaluate the benefits of CGM feedback throughout pregnancy in women without pre-existing Type I or Type II diabetes. The primary aim of this randomized controlled trial (RCT) study was to compare GDM outcomes and plasma glucose levels from the oral glucose tolerance test (OGTT) between users receiving CGM feedback and those who were not. The secondary aim was to compare maternal glycaemic control, and glycaemic variability in the first, second, late-second to early-third, and third trimesters of pregnancy between the two groups. We also explored user acceptability of both groups towards the use of their respective sensors. We hypothesize that receiving CGM feedback will result in lower OGTT glucose values, and a lower prevalence of GDM development (primary outcome) with improved glycaemic control and glycaemic variability parameters throughout pregnancy (secondary outcome).