Our study named Integrated Continuous glucose monitoring glycemic cHAracterization during Pregnancy in comparison with oral glucose tolerance test (I-CHAP) aims to establish much needed preliminary evidence in our Asian population to show the capabilities of CGM use and its wealth of data for GDM diagnosis. This study aims to test the following aims and hypotheses in a single-armed intervention pilot trial study of pregnant women undergoing the oral glucose tolerance test:

Aim 1. To characterize CGM glucose values with the 3-point blood glucose measured during the OGTT procedure.

The investigators hypothesize that the CGM glucose values at single time points while fasted, and after the 75-g glucose load will be positively correlated with 3-timepoint blood glucose values captured during the OGTT.

Aim 2. To correlate the CGM glucose excursions and CGM-derived metrics (glycaemic variability and glycaemic control) with maternal-fetal outcomes and treatment outcomes.

The investigators hypothesize that higher AUC, glycemic variability and poorer glycaemic control will better distinguish maternal-fetal outcomes and treatment outcomes, compared to the OGTT.

Aim 3. To describe the acceptability of using the Dexcom G6 CGM as a diagnostic tool instead of the OGTT. The investigators hypothesize that a higher proportion of participants will report CGM to be more acceptable than the OGTT for GDM diagnosis.

This proposal aims to address one of Singapore's major clinical challenges, which is the very high prevalence of GDM, and the current approach to GDM diagnosis. With the current practices, guidelines by the IADPSG, as well as the Singaporean guidelines recommend universal screening of GDM among all pregnant women at 24-28 weeks of gestation, which reveals the very high prevalence of GDM with 20-25% diagnosed by mid-pregnancy. The precision in GDM monitoring and treatment is important not only for the short-term adverse outcomes related to pregnancy and delivery, but as local studies have shown, also for the long-term consequences affecting both the mother and the child such as development of Type II Diabetes (T2D), obesity, metabolic, cardiovascular, neurodevelopment and psychiatric problems. While many patients can reach their target glucose levels through lifestyle behavior adjustments (diet and exercise), around 30% may require pharmacological interventions. Additionally, even individuals with only slightly elevated glucose levels, who don't meet the typical GDM criteria could experience better pregnancy outcomes if treated. This is because the connection between glucose levels and adverse pregnancy outcomes, such as macrosomia, remains consistent across a range of increasing glucose levels.

The primary gap in current research lies in the exploration of CGM use during pregnancy for diagnosing GDM, with the aim of leveraging the distinctive CGM glucose profiles to predict adverse maternal-fetal outcomes and advocate for a revised treatment approach. As CGM usage becomes increasingly accepted in clinical practice, there is a growing need for further research to advance this technology and explore the optimal ways to utilize the data it produces for improved GDM diagnosis and treatment strategies.

In this pilot single-arm intervention study, 60 pregnant women of only Chinese or Indian ethnicity with a GDM rate of 20% will be recruited from the KK Women's and Children's Hospital (KKH) outpatient obstetrics and gynaecology clinic. The participants recruited before scheduled OGTT's will be educated on how to put on the CGM after completing a consent form. Participants will be educated on how to put on the CGM device before their scheduled OGTTs at 20-35 weeks as an acclimation period and will undergo the OGTT before CGM removal on the 10th day of wear. Patients will be told to record the exact date and time of the OGTT. Exclusion criteria were pre-existing Type 1 or Type 2 diabetes, mental illness precluding informed consent and women who were diagnosed early (1st or early 2nd trimester for GDM).

Data will be collected through questionnaires and a case report form. The questionnaires include socio-economic factors, and baseline characteristics. The case report form will be collecting data on the OGTT glucose test results, as well as maternal obstetrics and birth outcomes.

Inclusion Criteria:

1. Pregnant women of only Chinese or Indian ethnicity
2. Pregnant women between age 21--45 years old
3. Oral glucose tolerance test (OGTT) to be scheduled between 20-35 weeks gestational age
4. OGTT to be done at KK Women's and Children's Hospital

Exclusion Criteria:

1. Women with serious skin conditions (e.g. eczema) that precludes wearing the sensor for 10 days
2. Exclusion criteria were pre-existing Type 1 or Type 2 diabetes, mental illness precluding informed consent and women who were diagnosed early (1st or early 2nd trimester for GDM).