Dr. Jacobson, from Kaiser Permanente Northern California, San Francisco, and colleagues compared glyburide and insulin treatment in nearly 600 women with singleton pregnancies who had gestational diabetes diagnosed by oral glucose tolerance test between 12 and 34 weeks gestation, a fasting plasma glucose of 140 mg/dL or less, and who failed diet therapy.

Women treated with glyburide had significantly lower mean fasting and postprandial blood sugar levels, the authors report in the July issue of the American Journal of Obstetrics and Gynecology. Maternal hypoglycemia was rare with both treatments but more common in the glyburide group (0.20%) than in the insulin group (0.08%).

Twenty-eight women (12%) in the glyburide group were switched to insulin, the report indicates, including 14 for poor control and 8 for side effects attributed to hypoglycemia.

Most maternal and neonatal outcomes were similar between treatments, the researchers note. Preeclampsia was more common in the glyburide group, and neonates in the glyburide group were more likely to receive phototherapy.

Neonates in the insulin group, however, were more likely to be admitted to the neonatal intensive care unit, the results indicate. There were no neonatal deaths, lethal anomalies, or exchange transfusions in either treatment group, the investigators report. Four infants in each group had congenital anomalies.

"Women should be switched to insulin if they are unable to achieve adequate glycemic control on glyburide," Dr. Jacobson advised.

Also, he emphasized, "It is important women (treated with glyburide) receive all the other standard prenatal, intrapartum, and postpartum care that would have been provided if they were on insulin, including frequency of visits, counseling, and antenatal surveillance."

The study findings show that "glyburide can be used to achieve good glycemic control in a large clinical setting in the majority of women with gestational diabetes unresponsive to dietary management," write Dr. Celeste Durnwald and Dr. Mark B. Landon from The Ohio State University Medical Center, Columbus, in a related editorial. "Larger trials will also be of benefit in describing clinical characteristics associated with glyburide failure."