Fetal macrosomia is a well-recognized adverse outcome associated with gestational diabetes. Weekly measurement of fasting and postprandial glucose should identify those with fasting (greater than or equal to 100 or 105 mg/dl) or postprandial (greater than or equal to 120 mg/dl 2 hours after a meal) hyperglycemia who are at increased risk for perinatal mortality. If the prevention of macrosomia is desired, the use of prophylactic insulin, initiated as early as possible, but at the latest before 36 weeks' gestation, without regard to glycemia is effective. Alternatively, glucose self-monitoring (four to six times daily with institution of insulin treatment when fasting glucose exceeds some arbitrary threshold such as 90 mg/dl or postprandial values exceed a threshold such as 100 mg/dl) is likely to be equally effective with fewer patients requiring insulin injections.