Glyburide Compared to Insulin in the Management of White's Classification A2 Gestational Diabetes

PLAN: Women who present for prenatal care are routinely screened for gestational diabetes (GDM) with a one-hour 50gm oral glucose challenge test (GCT). This screening occurs at the first prenatal visit if risk factors (marked obesity, prior pregnancy affected by GDM, prior macrosomic infant, glycosuria, strong family history of diabetes) for GDM are identified on intake history. If no risk factors for GDM are identified or if initial screening is negative, the GCT is administered between 24-28 weeks gestation. At our institution, the GCT is considered positive if, one hour after ingestion of a 50gm oral glucose solution, the serum glucose is greater than or equal to 135mg/dl. This screening cutoff varies among medical treatment facilities. Positive screening tests are followed by a diagnostic oral glucose tolerance test (GTT). A positive diagnosis requires that two or more thresholds be met or exceeded. Women with the diagnosis of gestational diabetes will receive dietary counseling and instruction on the performing capillary glucose from a by a nurse educator. If > 20% of recorded home glucose values are in excess of target range following initiation of appropriate diet, women will be offered enrollment into the study.

All women who agree to participate in the study will have an ultrasound performed to confirm gestational age and rule out fetal anomalies, a serum glycosylated hemoglobin A1C to assist in excluding preexisting diabetes and a fasting insulin level to assist in determining degree of insulin resistance. A serum glycosylated hemoglobin A1C will be repeated upon admission for delivery. Subjects randomized into standard therapy insulin arm will have their insulin dose calculated by established standards. Dosing is based upon a 2 shot combined dose with long acting and short acting insulin given prior to breakfast and dinner. If the fasting glucose values remain elevated the dinner NPH will be moved to bedtime. Subcutaneous administration is recommended in a consistent anatomic region, preferably the abdomen.

Insulin will be adjusted on a weekly basis in order to maintain optimal glucose control. Women assigned to receive glyburide will begin with 2.5mg orally with the morning meal. Glyburide dosage will be increased weekly as indicated to a maximum daily dose of 20mg to achieve glucose control. If the patient continues to have elevated fasting glucose the may be split to 12 hr intervals. If maximum daily dose of glyburide does not result in reaching the threshold values, patients will be administered insulin however data will be analyzed on an intent-to-treat basis.

Upon admission for delivery additional maternal blood will be collected for hemoglobin A1C, and glyburide levels. These values will be utilized to determine efficacy of treatment and for comparison to fetal umbilical cord values.

At delivery fetal blood from the umbilical cord will be collected for glucose, hematocrit, insulin level and, in a representative sample, glyburide level. These values will be utilized to determine whether insulin or glyburide provides superior efficacy in maintaining these values within normal limits. Cord blood glyburide levels will be obtained in a representative sample of exposed subjects.

When clinically indicated labs are performed by the pediatrician on the newborn, such as heel stick glucose for hypoglycemia, bilirubin levels for neonatal jaundice, calcium levels for suspected hypocalcemia, these values will be obtained by review of the newborn record.

In all gestational diabetics, post partum assessment of diabetic status will be assessed with either a fasting glucose determination or a 2hr glucose tolerance test .