June 22, 2007 — -- More pregnant women than believed may be at risk for a dangerous condition that can lead to difficult deliveries of huge babies, juvenile diabetes in the child, or severe birth defects.
This week, a large-scale study of pregnant women in nine countries showed that current guidelines for diagnosing a condition called gestational diabetes mellitus, or GDM, may be too generous, letting at-risk women fall through the cracks.
GDM -- which is essentially diabetes that occurs during pregnancy -- can lead to a whole host of problems for mother and baby. To learn more, Dr. Boyd Metzger, a professor of endocrinology at Northwestern University, led an international research team that studied more than 23,000 pregnant women around the globe from about 28 weeks until birth.
The moms to be had their blood sugar levels tested around 28 weeks of gestation. First, they had a fasting blood draw; then, they consumed sugar and had their blood drawn again after two hours. This "glucose tolerance test" is often used to confirm diabetes.
The scientists found that women with higher blood sugar levels were more likely to have very large babies and need a C-section.
In the group of moms with the lowest blood sugar, only 5 percent of the babies were in the top 10 percent in terms of size, while the 20 percent of the moms with the highest blood sugar had oversize babies.
The results were presented at the 67th Annual Meeting of the American Diabetes Association.
The study seems to hint that even women with borderline high blood sugar may be at risk for complications from GDM.
Women in the study who were found to have excessively high levels of blood sugar -- more than 105 milligrams per deciliter of blood fasting, or more than 200 after the glucose tolerance test -- were pulled from the study and treated for safety reasons.
But many of the remaining women whose sugar was on the "high side" but not high enough to keep them out of the study, experienced some of the same complications as women with GDM.
Metzger said he expects that, as a result of this study, the threshold for blood sugar levels in pregnant women may be lowered when it comes to testing for diabetes.
Diabetes is a disease of the pancreas -- a pistol-shaped organ in the abdomen responsible for making the hormone insulin, which helps the body store sugar.
In diabetics, the pancreas either can't make insulin anymore (type 1) or makes insulin that the body "resists" (type 2). Either way, without insulin the body has no way to store the food you eat.
Seventy percent of women with GDM develop full-blown diabetes within 10 years, meaning that they have blood sugar that needs to be controlled all the time.
But endocrinologists note that most cases of GDM are really regular diabetes that just gets discovered during prenatal OB appointments.
In a diabetic mother to be, the delicate hormonal balance that supports a growing fetus can be disrupted.
"In most mammals, insulin resistance increases in pregnancy," said Dr. Tom Buchanan, an endocrinologist who attended the diabetes meeting, adding that this is thought to be a way for more sugar to get to the blood of the hungry fetus.
But, in diabetic mothers, "the baby gets more glucose than it needs. That baby's insulin production goes up due to the increased exposure to blood sugar."
This is why, in addition to overweight babies, the study authors also found that when the babies were born, they tended to have dangerous drops in blood sugar soon after they were breast- or bottle-fed. Their bodies were literally soaking up nutrition at an abnormally high rate -- because they were used to it.
Treatments for GDM include dietary therapy, insulin or pills such as metformin and glyburide -- drugs that don't cross the placenta to the baby.
But are women with borderline-high blood sugar at risk for some of the worst outcomes, like birth defects?
Buchanan doesn't think so, since none of the women in the study had stillborn babies or babies who otherwise died at an early age.
Still, he emphasized that the more pregnant women are studied, the more we will know about what level of blood glucose is associated with problems at birth.
"The relative risk [for those with slightly above normal blood sugar] might be very small. … What we generally do in medicine is set a low threshold and treat everyone."