The purpose of this study is to compare the positive and negative effects of Dex4® tablets, as an alternative form of fast acting carbohydrate, compared to the current standard diagnostic test, glucose beverage. The investigators hypothesis that because of their availability in solid, chewable form, variety of flavours and lack of carbonation, Dex4® tablets may result in fewer side effects than glucose beverage and provide an equivalent carbohydrate challenge for diagnosis of gestational diabetes.

The project is a prospective randomized crossover study. Women who fall into the screen positive group of the 50g GCT (1 hour serum glucose of 7.8-11.0 mmol/L) will be offered participation in the study. Forty-two participants will be recruited and will be randomly assigned using a pre-populated allocation table to take either the standard OGTT test (75g of glucose beverage) first or the alternative OGTT test (21 Dex4® tablets) first. The first test will be referred to as OGTT-1 and the second test will be referred to as OGTT-2. After completing OGTT-1 at the first test appointment, a questionnaire about side effects from the first test will be completed. After completing OGTT-2 at their second test appointment, a questionnaire about side effects from the second test and test preference will be completed. Each woman will complete both tests within one week and each subject will serve as their own control. Results will be kept blinded in the case report forms until both OGTT tests are done. Serum glucose will be measured using the same internationally standardised glucose-oxidase method (RocheDiagnosis) in the Sunnybrook Biochemistry lab. After serum glucose measurement, all results will be sent to the research team but only the standard of care glucose beverage test data will appear in electronic (or classical) medical records and be used for GDM diagnosis.

The participant population consists of 28 pregnant women between 24-32 weeks' gestation who have screened positive for gestational diabetes on the 50g glucose challenge test. The main drawback to participation is that women will have to undergo two fasting, 1 hour and 2 hour glucose tests within one week. Risks involved with participating in the study include: possibility of pain, bruising, swelling or infection related to drawing blood, allergic reaction symptoms such as itching, facial swelling and anaphylaxis upon consumption if the participant has an allergy to corn based products such as dextrose. These risks will be minimized by screening patients for dextrose allergy before having them sign the informed consent form.

The benefit may not be directly to the patient as they will still need to complete the standard 75g glucose beverage test but they will be contributing to new knowledge on alternatives to the standard test that may benefit other pregnant women, including themselves, in the future.

The ultimate goal of this project is to improve women's health by 1) allowing more women to be screened for GDM and 2) providing an equivalent glucose beverage alternative with fewer side effects, making the screening process more comfortable for patients who cannot tolerate glucose beverage. Improving the tolerability of the test is important because there is growing evidence that GDM significantly increases the risk of short and long term adverse consequences for both the fetus and the mother (10,11). Accurate diagnosis may allow women to implement preventative measures such as a healthy lifestyle, which has shown to be effective in preventing T2DM in women with previous GDM (19,20). There have been recent quality control issues with the commercially available glucose beverage product (16), so this alternative test could become the standard test if the dose calibration is found to be more reliable.

Primary objective 1 (PO-1): to determine if Dex4® tablets is equivalent to glucose beverage for use in the 2-hr 75g OGTT in pregnant women between 24-32 weeks' gestation who have screened positive for GDM.

Secondary objective (SO-1): to determine if women have fewer side effects and prefer the standard (glucose beverage) OGTT test or the alternative (Dex4® tablets) OGTT test

Eligibility criteria must be met by 32 weeks' gestation to allow enrollment in the study.

Inclusion Criteria:

• Positive 50g GCT result between 7.8-11.0 mmol/L
• Female
• Singleton pregnancy
• Informed consent obtained and signed

Exclusion Criteria:

• Use of steroids, terbutaline, or metformin within the last 4 weeks
• Previous diagnosis of diabetes type 1 or 2 outside of pregnancy or diagnosis with any form of diabetes prior to 20 weeks of pregnancy
• Allergy to any ingredients (including the non-medicinal ingredients) in Dex4® tablets or Glucodex solution