Glyburide decreases blood sugar in gestational diabetes but not birth weight

All pregnant women undergo screening for gestational diabetes during the 24-28th week of pregnancy. For the 5-6% of women who are diagnosed with gestational diabetes by high blood sugars, physicians traditionally recommended diet modification or insulin to control blood sugar levels below the goal of 95 when fasting and 120 two hours after a meal. Mild gestational diabetes can often be controlled with diet modification, and in 2009, a large study demonstrated diet modification can improve maternal and neonatal outcomes for women with mild gestational diabetes. A new study from the University of Texas in Dallas examines the role of glyburide, an oral medicine to treat high blood sugar, in helping women with mild gestational diabetes.

395 women with mild gestational diabetes and otherwise uncomplicated pregnancies enrolled in the study. They all received standard nutritional counseling. Half of the women received glyburide 2.5mg daily and half the women received a placebo (a fake pill) that was designed to look like glyburide. The women's doctors increased the dose to try to control blood sugar. If blood sugar was still too high on a max dose of 20mg, the physician would start insulin. This tactic is consistent with the standard of care in obstetrics. 

The study authors estimated that the infants who received glyburide would weigh on average 200g less than the babies who did not receive the medication. Because diabetes can lead to infants who are "large for gestational age" (LGA) and prone to complications like the shoulder getting stuck during delivery and low blood sugar at birth, a 200g decrease in weight would be a benefit to these infants. The authors used this 200g estimation to decide how many women needed to enroll in the study- about 400- to make the study powerful enough to detect this possible positive effect of glyburide in reducing infants' weights. However, what they found was that infants weighted on average 33g less if their mother was treated with glyburide. This reduction was not significant. They also looked at other outcomes that may be related to having gestational diabetes: the need for a vacuum or forceps during delivery, the shoulder getting stuck during delivery, fracture of the shoulder bone during delivery, a nerve palsy, and low blood sugar at birth. None of these differed significantly between the two groups (although the study was not designed to be powerful enough to detect these differences). 

The one area in which glyburide did make a difference was maternal blood sugar control. Fasting blood sugar for women taking glyburide decreased by 7 on average while the fasting blood sugar levels of women taking the fake pill only decreased by 3. However, maternal weight gain was the same and the number of women whose treatments needed to be escalated to insulin was also the same in each group (4 each). Most women, whether they were taking glyburide or the fake pill, did not need to move on to insulin. In fact, the vast majority of women in the placebo group were able to control their blood sugar levels with diet modification alone.

This study contributes important information about the role of the oral diabetes medication glyburide for women with mild gestational diabetes. It shows that, although their blood sugar levels were lower, this did not improve their chances of avoiding insulin, having a infant who is LGA, or the poor outcomes associated with LGA.