Continuous Glucose Monitoring Versus Self-Monitoring of Blood Glucose in Women With Gestational Diabetes

Gestational diabetes mellitus (GDM) is a condition in which high blood glucose levels are first detected during pregnancy. It usually develops in the second or third trimester and affects a significant proportion of pregnant women worldwide. Although blood glucose levels often return to normal after delivery, GDM is associated with important short-term and long-term health risks for both the mother and the child.

In the short term, poorly controlled blood glucose levels during pregnancy increase the risk of excessive fetal growth (macrosomia or large for gestational age), shoulder dystocia, birth trauma, neonatal hypoglycemia, respiratory complications, and admission to the neonatal intensive care unit (NICU). For the mother, GDM increases the likelihood of hypertensive disorders of pregnancy, cesarean delivery, and postpartum complications. In the long term, women with GDM have a higher risk of developing type 2 diabetes and cardiovascular disease, and their children are at increased risk of obesity and metabolic disorders later in life.

Achieving and maintaining optimal glycemic control is therefore a central goal in the management of GDM. Standard treatment includes dietary counseling, physical activity recommendations, and regular monitoring of blood glucose levels. If lifestyle measures are not sufficient to reach glycemic targets, insulin therapy is initiated.

Currently, the standard method for glucose monitoring in women with GDM is self-monitoring of blood glucose (SMBG). This involves capillary finger-prick measurements typically performed four to six times per day (fasting and postprandial values). While SMBG provides important information, it has several limitations. It captures glucose levels only at specific time points and may miss significant fluctuations, including nocturnal hyperglycemia and postprandial excursions. It also relies heavily on patient adherence and accurate recording of results. Incomplete monitoring or reporting errors may affect clinical decision-making. Additionally, frequent finger pricks can be uncomfortable and burdensome.

Continuous glucose monitoring (CGM) offers an alternative approach. CGM systems use a small sensor inserted under the skin to measure interstitial glucose levels continuously throughout the day and night. The device provides real-time glucose readings, trend information, and metrics such as time in range, time above range, time below range, and glucose variability. These metrics offer a more comprehensive view of glycemic control than isolated capillary measurements.

In individuals with type 1 and type 2 diabetes, CGM has been shown to improve glycemic control, increase time in target range, reduce hypoglycemia, and enhance patient satisfaction. In pregnant women with type 1 diabetes, randomized clinical trials have demonstrated that CGM use can improve neonatal outcomes. However, evidence supporting the use of CGM in women with gestational diabetes remains limited and inconclusive. Observational studies suggest that CGM may detect glycemic abnormalities not captured by SMBG and may be associated with improved perinatal outcomes, but well-designed randomized controlled trials in this population are lacking.

This study aims to address this evidence gap.

Study Design

This is a single-center, parallel-group, pilot randomized controlled trial conducted at Hospital Clínic de Barcelona. The study will include pregnant women diagnosed with gestational diabetes between 24 and 28 weeks of gestation.

A total of 100 participants will be enrolled and randomly assigned in a 1:1 ratio to one of two groups:

Continuous Glucose Monitoring (CGM) Group

Self-Monitoring of Blood Glucose (SMBG) Group

Randomization will be computer-generated and implemented through a secure electronic system to ensure allocation concealment. Due to the nature of the intervention, participants cannot be blinded to group assignment; however, outcome assessors will be blinded when feasible.

Intervention

Participants in the CGM group will receive a CE-marked continuous glucose monitoring device (FreeStyle Libre 2). The device will be used according to the manufacturer's approved indications. Women will receive standardized training on sensor placement, device use, interpretation of glucose trends, and troubleshooting. A capillary glucose meter will also be provided for confirmation of values if necessary.

Participants in the SMBG group will continue with standard capillary glucose monitoring according to usual clinical practice, typically including fasting and postprandial measurements. They will receive standardized education on proper technique and documentation.

Both groups will receive identical clinical management, including dietary advice, physical activity recommendations, and insulin therapy initiation if glycemic targets are not achieved. Clinical decisions will follow established local protocols for gestational diabetes management. Follow-up visits will occur every 2 to 3 weeks until delivery, consistent with routine care.

No additional clinical visits beyond standard GDM management are required. Questionnaires assessing patient satisfaction and quality of life will be administered after two weeks of device use and again at delivery.

Objectives

The primary objective of this pilot study is to evaluate feasibility, including recruitment rate, retention rate, adherence to the assigned monitoring strategy, and completeness of collected data. In addition, preliminary efficacy data will be generated to estimate potential clinical benefits and inform the design of a future larger-scale randomized trial.

Secondary objectives include comparison between groups in:

Neonatal outcomes (birth weight, large for gestational age, neonatal hypoglycemia, NICU admission, obstetric trauma, Apgar scores, umbilical artery pH)

Maternal outcomes (need for insulin therapy, gestational age at insulin initiation, HbA1c levels, gestational weight gain, hypertensive disorders of pregnancy, postpartum hemorrhage, infections, and mode of delivery)

Glycemic control parameters (including CGM-derived metrics such as time in range and glucose variability)

Patient-reported outcomes, including treatment satisfaction, usability, and diabetes-related quality of life

Exploratory analyses will examine associations between CGM metrics and neonatal outcomes, as well as patient engagement with remote monitoring platforms.

Statistical Considerations

As a pilot trial, the sample size of 100 participants is designed to assess feasibility and generate preliminary estimates of effect size rather than to definitively demonstrate superiority. Analyses will follow the intention-to-treat principle. Continuous and categorical outcomes will be compared using appropriate statistical tests, and multivariable regression models will be used to adjust for potential confounders. Effect sizes and confidence intervals will be emphasized to inform future research planning.

Ethical and Regulatory Considerations

The study will be conducted in accordance with the Declaration of Helsinki and applicable European and Spanish regulations governing biomedical research and medical devices. The protocol and informed consent documents will be reviewed and approved by an independent Research Ethics Committee prior to study initiation.

Participation is voluntary. Written informed consent will be obtained before any study-specific procedures. Data will be coded and stored securely in compliance with the General Data Protection Regulation (GDPR). No biological samples will be collected as part of this study.

Significance

This pilot randomized clinical trial seeks to determine whether continuous glucose monitoring is feasible, acceptable, and potentially beneficial for women with gestational diabetes. By collecting comprehensive maternal, fetal, neonatal, and patient-reported data from diagnosis through delivery, the study will provide important preliminary evidence regarding the role of CGM in this population.

If results suggest clinical benefit and operational feasibility, the findings will support the development of a larger, adequately powered randomized controlled trial. Ultimately, this research aims to improve glycemic management strategies during pregnancy and enhance health outcomes for both mothers and their babies.

Inclusion criteria

• Pregnant women aged ≥18 years
• Singleton pregnancy
• Diagnosis of gestational diabetes mellitus (GDM) according to local two-step protocol (abnormal 50 g glucose challenge test followed by abnormal 100 g oral glucose tolerance test with at least 2 abnormal values)
• Gestational age between 24 and 28 weeks at time of GDM diagnosis
• Access to a compatible smartphone or digital device with internet connection to allow synchronization and remote upload of glucose data (CGM or SMBG)
• Ability and willingness to provide written informed consent

Exclusion criteria

• Preexisting type 1 or type 2 diabetes mellitus
• History of bariatric surgery
• Treatment with metformin during pregnancy
• Chronic systemic corticosteroid therapy
• Known contraindications to use of a CGM sensor (e.g., severe dermatologic conditions at insertion site)
• Inability to comply with study procedures or follow-up