EARLY Pregnancy GLucose prOfiles in Women With and Without GDM Risk Factors: EARLY-GLOW

The EARLY-GLOW study is a prospective, decentralized observational pilot study that aims to improve understanding of glucose regulation during early pregnancy and identify early signs of gestational diabetes mellitus (GDM) before conventional diagnosis. While current GDM screening relies primarily on an oral glucose tolerance test (OGTT) performed between 24 and 28 weeks of gestation, growing evidence suggests that disturbances in glucose metabolism may already be detectable much earlier in pregnancy. Continuous glucose monitoring (CGM) offers the opportunity to capture detailed glucose patterns throughout the day and may reveal subtle abnormalities that are not identified through standard screening methods.

The study will recruit 48 pregnant women with singleton pregnancies at approximately 12 weeks of gestation from across Switzerland. Participants will be stratified into two groups: women with at least one established risk factor for GDM and women without known risk factors. Risk factors include obesity, previous gestational diabetes, a family history of type 2 diabetes, polycystic ovary syndrome, previous macrosomic offspring, bariatric surgery, and certain ethnic backgrounds associated with increased GDM risk.

After enrolment, participants will wear a blinded Dexcom G7 continuous glucose monitor for approximately 12 to 16 weeks, covering the period from early pregnancy until routine GDM screening. Because the sensor is blinded, participants will not be able to see their glucose values during the main observation period, minimizing the risk that knowledge of glucose levels influences behavior. At regular intervals, participants will also record fasting blood glucose measurements, upload meal photos, document nutritional intake, and complete questionnaires regarding sleep, stress, well-being, physical activity, and pregnancy-related symptoms. During the final two weeks of follow-up, participants may additionally wear an unblinded FreeStyle Libre 3 sensor to evaluate user experience and compare acceptance of the two most commonly used CGM systems in Switzerland.

The primary objective of the study is to identify CGM-derived thresholds that characterize early dysglycemia in pregnancy. Rather than focusing solely on a glucose value, the study aims to determine combinations of glucose level and duration of exposure that best distinguish women with and without GDM risk factors. This approach acknowledges that the clinical significance of elevated glucose levels may depend not only on how high glucose rises, but also on how long those elevations persist.

Secondary objectives include comparing the frequency and duration of hyperglycemic episodes between risk groups, assessing time spent above and below target glucose ranges, evaluating measures of glycemic variability, and characterizing postprandial and nocturnal glucose patterns. The study will also investigate the relationship between glucose profiles and lifestyle factors such as diet, sleep quality, physical activity, stress, and well-being. Furthermore, participant adherence, device wear time, comfort, usability, and acceptance of the CGM systems will be assessed to determine the feasibility of large-scale CGM use during pregnancy.

To analyze the data, researchers will use both traditional statistical methods and exploratory pattern-recognition techniques. Receiver operating characteristic (ROC) analyses will be applied to identify glucose thresholds and durations that best discriminate between women at higher and lower risk of GDM. In addition, clustering and glucose-profile analyses will be used to describe different glycemic phenotypes during pregnancy and to identify potentially clinically relevant patterns.

The study is observational, no therapeutic interventions are performed. Participants may benefit indirectly from the nutritional consultation offered at the end of the study, during which glucose data and dietary habits are reviewed with a nutrition specialist. More importantly, the knowledge generated by the study may contribute to improved screening strategies, earlier identification of women at risk for GDM, and the future development of personalized preventive interventions.

Inclusion criteria

• Female sex
• Aged ≥18 years at inclusion
• Pregnant with singleton ≤12 GW
• Willingness to wear a CGM device for 12-16 weeks
• Signed informed consent

Exclusion criteria

• Pre-existing type 1 or type 2 diabetes mellitus or known prediabetes
• Diagnosis of GDM during current pregnancy
• Known allergy to adhesive materials or sensor components
• Inability to follow procedures or insufficient knowledge of project languages (German, French or English)
• Inability to give consent.