Healthy eating during pregnancy has favorable effects on markers related to diabetes (glucose tolerance) and is associated with lower gestational diabetes mellitus (GDM) risk. The cornerstone of GDM treatment is nutrition therapy but the latter often starts late in pregnancy and thus may not have the expected effects on glucose tolerance. What if an intervention promoting healthy eating was initiated at the beginning of pregnancy in all women at risk, would it improve glucose homeostasis? To answer this important question, the investigators will perform a randomized controlled trial in 150 pregnant women. Women receiving the nutritional intervention will be compared to a control group receiving standard care. The nutritional intervention, which will start in the first trimester, is based on the 2019 Canada's Food Guide and is composed of 4 individual sessions with a registered dietitian (12, 18, 24 and 30 weeks). Between those follow-ups, informative nutritional web capsules and phone calls with the registered dietitian will be provided. To ensure that the women remain motivated and receive social support, a private Facebook group will be used. The investigators hypothesize that the nutritional intervention will be effective at improving glucose homeostasis. The investigators expect the results will show the importance of nutritional care starting early in pregnancy in women at risk of GDM.

Individuals will participate in three on-site research visits during which a 2-hour oral glucose tolerance test will be performed. At each of these trimesters and 3 months after the delivery, participants will also complete three validated web-based 24-h recalls from which diet quality will be assessed. Subjects will be randomized to two arms after the first oral glucose tolerance test at the first visit. For all participants, on-site follow-ups by the research team will occur at each trimester and 1 virtual follow-up will be done 3 months after delivery for both groups. The total duration of participation for all is approximately 9 months.

Inclusion Criteria:

• ≤ 14 gestational weeks;
• Singleton pregnancy;
• At risk of GDM According to Diabetes Canada (being 35 years of age or older or from a high-risk group (African, Arab, Asian, Hispanic, Indigenous, or South Asian) or having a BMI ≥ 30 kg/m2, prediabetes, GDM in a previous pregnancy, given birth to a baby that weighed more than 4 kg, a parent, brother or sister with type 2 diabetes, polycystic ovary syndrome or acanthosis nigricans (darkened patches of skin).

Exclusion Criteria:

• Having a diabetes diagnosis in the 1st trimester;
• Pre-existing diabetes mellitus;
• Diseases requiring active nutritional treatment or influencing glucose metabolism (including previous bariatric surgery);
• Taking part in a nutritional intervention program;
• Corticosteroid use;
• Previous or current diagnosis of an eating disorder;
• Inability to give informed consent;
• Inability to communicate in French.