Randomized Controlled Trial Investigating the Effects of a Low– Glycemic Index Diet on Pregnancy Outcomes in Women at High Risk of Gestational Diabetes Mellitus: The GI Baby 3 Study Diabetes Care 2016;39:31–38 | DOI: 10.2337/dc15-0572 OBJECTIVE Dietary interventions can improve pregnancy outcomes in women with gesta- tional diabetes mellitus (GDM). We compared the effect of a low–glycemic index (GI) versus a conventional high-fiber (HF) diet on pregnancy outcomes, birth weight z score, and maternal metabolic profile in women at high risk of GDM. RESEARCH DESIGN AND METHODS One hundred thirty-nine women [mean (SD) age 34.7 (0.4) years and prepreg- nancy BMI 25.2 (0.5) kg/m 2 ] were randomly assigned to a low-GI (LGI) diet (n= 72; target GI ∼50) or a high-fiber, moderate-GI (HF) diet (n = 67; target GI ∼60) at 14– 20 weeks’ gestation. Diet was assessed by 3-day food records and infant body composition by air-displacement plethysmography, and pregnancy outcomes were assessed from medical records. RESULTS The LGI group achieved a lower GI than the HF group [mean (SD) 50 (5) vs. 58 (5); P < 0.001]. There were no differences in glycosylated hemoglobin, fructosamine, or lipids at 36 weeks or differences in birth weight [LGI 3.4 (0.4) kg vs. HF 3.4 (0.5) kg; P = 0.514], birth weight z score [LGI 0.31 (0.90) vs. HF 0.24 (1.07); P= 0.697], ponderal index [LGI 2.71 (0.22) vs. HF 2.69 (0.23) kg/m 3 ; P = 0.672], birth weight centile [LGI 46.2 (25.4) vs. HF 41.8 (25.6); P = 0.330], % fat mass [LGI 10 (4) vs. HF 10 (4); P = 0.789], or incidence of GDM. CONCLUSIONS In intensively monitored women at risk for GDM, a low-GI diet and a healthy diet produce similar pregnancy outcomes. Gestational diabetes mellitus (GDM) is defined as carbohydrate intolerance that is diagnosed for the first time in pregnancy (1). Pregnancy-related hormonal changes that reduce insulin sensitivity result in glucose intolerance in women with reduced b-cell reserve or with more marked underlying insulin resistance. Glucose intoler- ance in pregnancy has implications for both mother and child, including higher rates of preeclampsia, operative deliveries, macrosomia, and birth injury (2). 1 The Boden Institute of Obesity, Nutrition, Exer- cise & Eating Disorders, Sydney Medical School, The University of Sydney, Sydney, NSW, Australia 2 Department of Endocrinology, Royal Prince Alfred Hospital, Camperdown, NSW, Australia 3 Charles Perkins Centre, The University of Syd- ney, Sydney, NSW, Australia 4 School of Molecular Bioscience, The University of Sydney, Sydney, NSW, Australia 5 Sydney Medical School, The University of Syd- ney, Sydney, NSW, Australia 6 Department of Statistics, Macquarie University, Sydney, NSW, Australia 7 RPA Women and Babies, Royal Prince Alfred Hospital, Camperdown, NSW, Australia Corresponding author: Tania P. Markovic, tania. markovic@sydney.edu.au. Received 23 March 2015 and accepted 22 June 2015. Clinical trial reg. no. ACTRN12610000681055, anzctr.org.au. © 2016 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered. See accompanying articles, pp. 13, 16, 24, 39, 43, 50, 53, 55, 61, and 65. Tania P. Markovic, 1,2 Ros Muirhead, 1,3,4 Shannon Overs, 1,3,4 Glynis P. Ross, 2,5 Jimmy Chun Yu Louie, 1,3,4 Nathalie Kizirian, 1,3,4 Gareth Denyer, 3,4 Peter Petocz, 6 Jon Hyett, 7 and Jennie C. Brand-Miller 1,3,4 Diabetes Care Volume 39, January 2016 31 MANAGEMENT OF GESTATIONAL DIABETES MELLITUS