OBJECTIVE—To compare management based on maternal glycemic criteria with management based on relaxed glycemic criteria and fetal abdominal circumference (AC) measurements in order to select patients for insulin treatment of gestational diabetes mellitus (GDM) with fasting hyperglycemia. RESEARCH DESIGN AND METHODS—In a pilot study, 98 women with fasting plasma glucose (FPG) concentrations of 105–120 mg/dl were randomized. The standard group received insulin treatment. The experimental group received insulin if the AC, measured monthly, was ≥70th percentile and/or if any venous FPG measurement was >120 mg/dl. Power was projected to detect a 250-g difference in birth weights. RESULTS—Gestational ages, maternal glycemia, and AC percentiles were similar at randomization. After initiation of protocol, venous FPG (P = 0.003) and capillary blood glucose levels (P = 0.049) were significantly lower in the standard group. Birth weights (3,271 ± 458 vs. 3,369 ± 461 g), frequencies of birth weights >90th percentile (6.3 vs 8.3%), and neonatal morbidity (25 vs. 25%) did not differ significantly between the standard and experimental groups, respectively. The cesarean delivery rate was significantly lower (14.6 vs. 33.3%, P = 0.03) in the standard group; this difference was not explained by birth weights. In the experimental group, infants of women who did not receive insulin had lower birth weights than infants of mothers treated with insulin (3,180 ± 425 vs. 3,482 ± 451 g, P = 0.03). CONCLUSIONS—In women with GDM and fasting hyperglycemia, glucose plus fetal AC measurements identified pregnancies at low risk for macrosomia and resulted in the avoidance of insulin therapy in 38% of patients without increasing rates of neonatal morbidity.