Pregnancy is a critical window for metabolic health, and early changes in blood sugar regulation can increase the risk of gestational diabetes mellitus (GDM), which affects both maternal and infant health. At the same time, the maternal gut microbiome changes throughout pregnancy and may play a role in glucose metabolism and insulin resistance. Kefir, a fermented milk drink containing beneficial bacteria and yeasts, may be a simple dietary strategy to support metabolic health during pregnancy, but its role in preventing GDM has not been well studied.

This study will test whether drinking kefir daily from mid-pregnancy until routine GDM screening can improve glucose and insulin regulation, reduce the incidence of GDM, and modulate the maternal gut microbiome and metabolites, among other outcomes.

Pregnant individuals will be randomly assigned to either a kefir group or a control group receiving usual prenatal care. Researchers will collect blood glucose and insulin measures, dietary information, stool samples, and body composition data across pregnancy and postpartum to evaluate metabolic and microbiome-related changes.

As one of the first studies to examine kefir as an early pregnancy intervention for GDM prevention, this study will help clarify whether a practical, food-based approach can improve maternal metabolic health. The findings may support future nutrition strategies aimed at reducing GDM risk and improving pregnancy outcomes.

Pregnancy is characterized by progressive metabolic and hormonal changes, including increasing insulin resistance, particularly in the second trimester. At the same time, the maternal gut microbiome undergoes substantial shifts across gestation and may contribute to glucose metabolism, insulin resistance, and inflammation. Dietary strategies that can favorably influence the gut microbiome and metabolic health during pregnancy may represent a promising approach to reduce GDM risk. Kefir, a fermented dairy beverage containing a complex consortium of beneficial bacteria and yeasts, has shown potential for improving glycemic control and modulating the gut microbiome in non-pregnant populations, but its preventive role for GDM has not been well established.

The primary aims of this study are to determine whether daily kefir consumption initiated in mid-pregnancy can improve maternal glucose and insulin regulation. Secondary aims will examine whether kefir consumption reduces the incidence of GDM, beneficially modulates maternal gut microbiome and metabolite profiles, and alters postpartum health measures such as breastmilk composition and infant anthropometrics.

This randomized controlled trial in the PEADS Lab at the University of New Brunswick will assign pregnant participants to either a daily kefir intervention group or a control group receiving usual prenatal care. Participants in the intervention group will consume 250 mL of kefir daily beginning at approximately 14 weeks' gestation and continuing until the routine GDM screening window at 26-28 weeks' gestation. Those in the control group will continue with their usual care and habitual diet, but will be asked not to consume kefir for the duration of the study. Participants will attend study visits across pregnancy and postpartum, during which researchers will collect dietary recalls, anthropometric and body composition measurements, blood pressure, and stool and breastmilk samples. Fasted clinical bloodwork will be used to assess glucose and insulin-related outcomes, including screening for GDM.

The primary outcomes are between-group differences in maternal glycemic and insulinemic measures. Secondary outcomes include the incidence of GDM, changes in gut microbial diversity, composition, and metabolites such as short-chain fatty acid concentrations, maternal body composition, breastmilk composition, and infant anthropometrics. Assessments will occur at baseline (~14 weeks gestation), at the GDM screening windows (18-20 weeks for high-risk and 26-28 weeks for low-risk), and one month postpartum.

Pregnancy represents a critical opportunity for early prevention of metabolic complications that can affect lifelong maternal and child health. This study is the first to evaluate kefir as a practical, food-based intervention for GDM prevention, while also exploring the role of the gut microbiome as a potential modifiable mechanism. By integrating clinical, dietary, and microbiome data, this trial will help generate evidence to support accessible nutrition strategies that may improve pregnancy outcomes and inform future maternal health recommendations.

Inclusion Criteria:

• Pregnant individual with a singleton pregnancy
• 19 years and older of age
• Gestational age 14,3 weeks or less at enrolment
• Able and willing to attend four in-person study visits at the PEADS Laboratory: baseline, 18-20 weeks' gestation, 26-28 weeks' gestation, and 1 month postpartum
• Willing and able to comply with study group assignment, including daily consumption of 250 mL of kefir if assigned to the intervention group
• Willing to avoid kefir consumption until completion of the 26-28-week study visit if assigned to the control group
• Willing to provide required biological and clinical samples, including stool samples and glucose/insulin data, according to the study protocol
• No probiotic, prebiotic, synbiotic, or antibiotic use during the first trimester or at enrollment
• Not currently consuming probiotic, prebiotic, synbiotic, or antiobiotic supplements
• Willing to avoid probiotic, prebiotic, and synbiotic supplements until completion of the 26-28-week study visit.
• Does not engage in regular moderate-to-vigorous physical activity
• No recent or active infectious illness or significant gastrointestinal symptoms, including diarrhea or constipation in the first trimester of pregnancy.
• No history of bariatric surgery
• Able to communicate in English or French
• Currently living in Fredericton, New Brunswick, and not planning to relocate before the 1-month postpartum visit

Exclusion Criteria:

• Pre-existing metabolic disease affecting glucose regulation, including type 1 diabetes or type 2 diabetes
• Current use or first trimester use of medications known to alter glucose metabolism, such as metformin or semaglutide
• Gastrointestinal or inflammatory disease, including Crohn's disease, ulcerative colitis, celiac disease, or diagnosed irritable bowel syndrome
• Allergy, intolerance, or other contraindication to dairy or components of kefir