The mainstay of management for gestational diabetic women (GDM) has been dietary. If it is inadequate to sustain normoglycemia, insulin therapy must be initiated. We studied whether we could prevent macrosomia by insulin therapy based on four daily self blood glucose levels (SBG). Fifty GDM, ages 28-39 years were, recruited to the study. They were divided based on fasting glucose (FBS) level on the glucose tolerance test (GTT): those with FBS less than 90 mg/dl were managed by diet alone; those with FBS greater than 90 mg/dl were immediately started on insulin. The four SBG checks [FBS and 1 hour after each meal (lhpc)] correlated with the continuous glucose monitor with r = 0.91. The women were asked to perform a dipstick for ketones on their urine upon awakening and whenever a meal or snack had been missed. Insulin was initiated when the SBG monitoring indicated that: (1) the FBS was 80 mg/dl whole blood from fingerstick (WBG) or the plasma glucose (PG) greater than 90 mg/dl and/or (2) the lhpc was greater than 140 mg/dl WBG and/or (3) the patient had persistent ketonuria on the prescribed diet which cleared only when the caloric intake was increased to a point which precipitated postprandial hyperglycemia. The prescribed diet was calculated based on body weight to be 30 kcal/kg if the women were between 80 and 120% ideal body weight; or was calculated to be 24 kcal/kg if their weight was greater than 120% ideal body weight. The calories were divided such that 40% was carbohydrate, 20% protein, and 40% fat.(ABSTRACT TRUNCATED AT 250 WORDS)