Women were invited to participate in this study if, between 24 weeks 0 days and 30 weeks 6 days of gestation, they had a blood glucose concentration between 135 and 200 mg per deciliter (between 7.5 and 11.1 mmol per liter) 1 hour after a 50-g glucose loading test. Women were excluded if they had preexisting diabetes, an abnormal result on a glucose screening test before 24 weeks of gestation, prior gestational diabetes, a history of stillbirth, multifetal gestation, asthma, or chronic hypertension; if they were taking corticosteroids; if there was a known fetal anomaly; or if imminent or preterm delivery was likely because of maternal disease or fetal conditions. All the women who pa rticipated in the study provided written informed consent. The study was approved by the human subjects committee at each participating center.
After an overnight fast, eligible women completed a blinded 3-hour 100-g oral glucose-tolerance test. Samples were analyzed at a central laboratory, and results were forwarded to the data coordinating center. Mild gestational diabetes mellitus was defined as a fasting glucose level of less than 95 mg per deciliter (5.3 mmol per liter) and two or three timed glucose measurements that exceeded established thresholds: 1-hour, 180 mg per deciliter (10.0 mmol per liter); 2-hour, 155 mg per deciliter (8.6 mmol per liter); and 3-hour, 140 mg per deciliter (7.8 mmol per liter).10 (link) Women who met these criteria were randomly assigned by the coordinating center, with the use of the simple urn method,11 (link) stratified by clinical center. The urn method minimizes the degree of imbalance in the number of patients assigned to each group by increasing the probability of a patient’s assignment to the group that has previously been selected least often. Women were assigned to receive either formal nutritional counseling and diet therapy,12 (link) along with insulin if required (treatment group) or usual prenatal care (control group). In addition, a cohort of women who had a positive result on the 50-g glucose loading test but a normal result on a subsequent oral glucose-tolerance test and who were matched with the study cohort according to race and body-mass index (the weight in kilograms divided by the square of the height in meters), dichotomized as less than 27 or 27 or more, were enrolled by the data coordinating center in the group that received usual prenatal care. By including this group of women who did not have gestational diabetes mellitus, the patients, their caregivers, and the study staff were unaware of whether women in the control group met the criteria for the diagnosis of mild gestational diabetes mellitus. Women with a fasting glucose level of 95 mg per deciliter or more on the diagnostic oral glucose-tolerance test were excluded from the study, and their condition was made known to their health care providers.
Ultrasonography was performed in all subjects before the oral glucose-tolerance test to confirm the gestational age. Women who were receiving treatment performed daily self-monitoring of their blood glucose (fasting and 2-hour postprandial measurements) with the use of a portable memory-based reflectance meter. Insulin was prescribed if the majority of fasting values or postprandial values between study visits were elevated (fasting glucose level, ≥95 mg per deciliter or 2-hour postprandial glucose level, ≥120 mg per deciliter [6.7 mmol per liter]). If, during a prenatal visit, there was a clinical suspicion of hyperglycemia in a patient who was in the control group, the blood glucose level could be measured at the discretion of the provider. If a random blood glucose level of 160 mg per deciliter (8.9 mmol per liter) or more or a fasting glucose level of 95 mg per deciliter or more was detected, the patient’s caregiver initiated treatment and notified the local principal investigator and study personnel.
Nonstress testing, biophysical profile testing, and ultrasonography to assess fetal growth were not performed routinely in the treatment group but were reserved for standard obstetrical indications. However, all the women who were enrolled in the study were instructed regarding the daily assessment of fetal activity.13 (link) If delivery was not the result of spontaneous labor, the rationale for the timing and method of delivery was documented.
After an overnight fast, eligible women completed a blinded 3-hour 100-g oral glucose-tolerance test. Samples were analyzed at a central laboratory, and results were forwarded to the data coordinating center. Mild gestational diabetes mellitus was defined as a fasting glucose level of less than 95 mg per deciliter (5.3 mmol per liter) and two or three timed glucose measurements that exceeded established thresholds: 1-hour, 180 mg per deciliter (10.0 mmol per liter); 2-hour, 155 mg per deciliter (8.6 mmol per liter); and 3-hour, 140 mg per deciliter (7.8 mmol per liter).10 (link) Women who met these criteria were randomly assigned by the coordinating center, with the use of the simple urn method,11 (link) stratified by clinical center. The urn method minimizes the degree of imbalance in the number of patients assigned to each group by increasing the probability of a patient’s assignment to the group that has previously been selected least often. Women were assigned to receive either formal nutritional counseling and diet therapy,12 (link) along with insulin if required (treatment group) or usual prenatal care (control group). In addition, a cohort of women who had a positive result on the 50-g glucose loading test but a normal result on a subsequent oral glucose-tolerance test and who were matched with the study cohort according to race and body-mass index (the weight in kilograms divided by the square of the height in meters), dichotomized as less than 27 or 27 or more, were enrolled by the data coordinating center in the group that received usual prenatal care. By including this group of women who did not have gestational diabetes mellitus, the patients, their caregivers, and the study staff were unaware of whether women in the control group met the criteria for the diagnosis of mild gestational diabetes mellitus. Women with a fasting glucose level of 95 mg per deciliter or more on the diagnostic oral glucose-tolerance test were excluded from the study, and their condition was made known to their health care providers.
Ultrasonography was performed in all subjects before the oral glucose-tolerance test to confirm the gestational age. Women who were receiving treatment performed daily self-monitoring of their blood glucose (fasting and 2-hour postprandial measurements) with the use of a portable memory-based reflectance meter. Insulin was prescribed if the majority of fasting values or postprandial values between study visits were elevated (fasting glucose level, ≥95 mg per deciliter or 2-hour postprandial glucose level, ≥120 mg per deciliter [6.7 mmol per liter]). If, during a prenatal visit, there was a clinical suspicion of hyperglycemia in a patient who was in the control group, the blood glucose level could be measured at the discretion of the provider. If a random blood glucose level of 160 mg per deciliter (8.9 mmol per liter) or more or a fasting glucose level of 95 mg per deciliter or more was detected, the patient’s caregiver initiated treatment and notified the local principal investigator and study personnel.
Nonstress testing, biophysical profile testing, and ultrasonography to assess fetal growth were not performed routinely in the treatment group but were reserved for standard obstetrical indications. However, all the women who were enrolled in the study were instructed regarding the daily assessment of fetal activity.13 (link) If delivery was not the result of spontaneous labor, the rationale for the timing and method of delivery was documented.