OBJECTIVE Given the role of gut microbiota in regulating metabolism, probiotics administered during pregnancy might prevent gestational diabetes mellitus (GDM). This question has not previously been studied in high-risk overweight and obese pregnant women. We aimed to determine whether probiotics (Lactobacillus rhamnosus and Bifidobacterium animalis subspecies lactis [BB-12]) administered from the second trimester in overweight and obese women prevent GDM as assessed by an oral glucose tolerance test (OGTT) at 28 weeks’ gestation. Secondary outcomes included maternal and neonatal complications, maternal blood pressure and BMI, and infant body composition.

RESEARCH DESIGN AND METHODS This was a double-blind randomized controlled trial of probiotic versus placebo in overweight and obese pregnant women in Brisbane, Australia.

RESULTS The study was completed in 411 women. GDM occurred in 12.3% (25 of 204) in the placebo arm and 18.4% (38 of 207) in the probiotics arm (P = 0.10). At OGTT, mean fasting glucose was higher in women randomized to probiotics (79.3 mg/dL) compared with placebo (77.5 mg/dL) (P = 0.049). One- and two-hour glucose measures were similar. Preeclampsia occurred in 9.2% of women randomized to probiotics compared with 4.9% in the placebo arm (P = 0.09). Excessive weight gain occurred in 32.5% of women in the probiotics arm (55 of 169) compared with 46% in the placebo arm (81 of 176) (P = 0.01). Rates of small for gestational age (<10th percentile) were 2.4% in the probiotics arm (5 of 205) and 6.5% in the placebo arm (13 of 199) (P = 0.042). There were no differences in other secondary outcomes.

CONCLUSIONS The probiotics used in this study did not prevent GDM in overweight and obese pregnant women.