Pregnancy: High-Normal Blood Sugar Risky

Experts Question Whether Gestational Diabetes Limit Is Too High

Reviewed by Louise Chang, MD on May 07, 2008

May 7, 2008 -- Babies born to women with even slightly higher-than-normal blood sugar levels are at increased risk for a range of pregnancy and delivery-related complications, findings from an international study confirm.

The large study examined the risks associated with having elevated blood sugar during pregnancy that is not high enough to be considered gestational diabetes.

More than 25,000 pregnant women from nine countries took part in the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study, which appears in the May 8 issue of The New England Journal of Medicine and was largely funded by the National Institutes of Health.

Even a small rise in blood sugar above what is considered normal was associated with an increase in adverse outcomes, including high birth weight, C-section delivery, and preeclampsia, a complication that can lead to premature birth and can be deadly if not treated.

The findings make it clear that elevated blood sugar has a direct negative impact on pregnancy and delivery, study co-author Donald R. Coustan, MD, tells WebMD.

Coustan is professor and chairman of obstetrics and gynecology at Brown University Medical School.

"This lays to rest many of the criticisms about gestational diabetes treatment," Coustan says. "The critics have said that it isn't elevated glucose that leads to negative outcomes, it is obesity or maternal age or some other risk factor. But we were able to control for these risk factors, and glucose was still a major determinant of outcomes."

Who Should Be Treated?

One important question that remains unanswered is whether the threshold for treating high blood sugar in pregnancy should be lowered and if so, by how much.

"Because there was a continuous relationship that was even seen in women with glucose levels considered near normal, this study isn't very helpful for trying to pinpoint where the cutoff should be," Coustan says.

In an editorial accompanying the study, diabetes researchers Jeffrey Ecker, MD, and Michael Greene, MD, of Harvard Medical School, conclude that the current evidence does not support lowering the threshold for gestational diabetes diagnosis and treatment.

While women in the HAPO trial with higher blood sugar levels also had higher rates of delivering high birth-weight babies, they also gave birth to fewer babies who were small for their gestational age.

And while C-section rates increased with increasing blood sugar in the HAPO study, the increase was modest. Treatment to lower blood sugar levels was found to have no impact on C-section deliveries in a similar study of pregnant women with high-normal blood sugar.

"Until trials show clinical benefits for expanding the diagnostic criteria for 'gestational diabetes,' we would not favor any change," Ecker and Greene write.

Next month, an internationally representative group of diabetes, pregnancy, and public health experts will meet in Pasadena, Calif., to make their own assessment.

"Right now, there is a total lack of agreement about what should be called gestational diabetes and who should be treated," HAPO project manager Lynn P. Lowe, PhD, of Northwestern University tells WebMD.

Is Metformin Safe?

There is also confusion about which blood sugar-lowering therapies are best for the treatment of gestational diabetes.

Insulin is often recommended when diet and exercise alone fail to lower blood sugar, but use of the widely prescribed diabetes drug metformin during pregnancy remains controversial.

In a separate study also reported in Thursday's New England Journal of Medicine, researchers compared outcomes in 751 women with gestational diabetes treated with either insulin or metformin.

Researcher Janet A. Rowan, MB, and colleagues reported no increase in complications among infants born to mothers who took metformin.

But almost half (46%) of the metformin-treated women ended up needing supplemental insulin.

Show Sources


HAPO Study Cooperative Research Group report and the Metformin in Gestational Diabetes Trial, The New England Journal of Medicine, May 8, 2008; vol 358: pp 1991-2002.

Lynn P. Lowe, PhD, epidemiologist, Northwestern University Feinberg School of Medicine, Chicago.

Donald R. Coustan, MD, professor and chairman, department of obstetrics and gynecology, Brown University Medical School, Providence, R.I.

The ACHOIS trial, The New England Journal of Medicine, 2005; vol 352: pp 2477-2486.

Rowan, J. The New England Journal of Medicine, May 8, 2008; vol 358: pp 2003-2015.

Ecker, J. and Greene, M. The New England Journal of Medicine; vol 358: pp 2061-2063.

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