Assessing gestational diabetes risks—for mom and baby

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Previous diagnostic criteria for gestational diabetes were based on the risk, posed by high blood sugar levels, that pregnant women faced for developing diabetes after giving birth. And, under those criteria, rates of gestational diabetes have surged nearly 50% in the past decade, with 5% to 8% of pregnant women being diagnosed with the condition. Yet, findings from a large-scale study published in the New England Journal of Medicine in May 2008 suggested that existing diagnostic criteria may actually leave out many women, and babies, at risk of health complications due to gestational diabetes. Authors of that 2008 study, led by Dr. Boyd E. Metzger, an endocrinologist at Northwestern University’s Feinberg School of Medicine, concluded that, even below the threshold for a diabetes diagnosis, there were strong correlations between high maternal blood sugar levels and risks for serious complications, ranging from high insulin levels among babies to the risk for preeclampsia, or high maternal blood pressure that can seriously jeopardize the baby’s health and safety.

Those findings, based on data from some 23,000 women from nine different countries participating in the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study, led researchers to develop new diagnostic criteria for gestational diabetes, based on what blood sugar levels would indicate nearly double the risk of complications for both mother and baby. Under the new guidelines, a fasting blood sugar level (the amount of sugar in your blood when you haven’t eaten for at least eight hours) of 92 or higher, of 180 or higher on a glucose tolerance test one hour after a meal or 153 on a glucose tolerance test two hours after a meal would meet the threshold for gestational diabetes.

At those levels, the occurrence of preeclampsia is nearly double, the frequency of giving birth to overweight babies is nearly double, and likelihood of giving birth early is 40% higher, Metzger points out. Previously, however, those measurements were considered to be in the healthy range.

Under new criteria incorporating this broader range of risk, gestational diabetes cases are expected to double or even triple, according to new research led by Dr. Metzger and published in the March issue of the journal Diabetes Care. With new diagnostic criteria, 16% of women—up from the previous 5% to 8%—meet the threshold for gestational diabetes.

Black, Hispanic, Asian and Native American women are more likely to develop gestational diabetes than women of other ethnicities, as are women over age 25, or who have a family history of diabetes. Additionally, women who are significantly overweight, particularly those who have a Body Mass Index (BMI) of 30 or higher, are at heightened risk for gestational diabetes. (A 5’4″ woman who weighs 175 lbs. has a BMI of 30, for example.) And, new research published this week in the journal Obstetrics & Gynecology suggests that women who gain large amounts of weight during the first trimester of pregnancy—beyond the pregnancy weight gain levels recommended by the Institute of Medicine (IOM)—were at 50% higher risk for gestational diabetes compared with those whose weight gain fell within, or below, the IOM recommendations.

The IOM guidelines suggest that, during the course of a pregnancy, women with a BMI between 18.5 to 24.9 (normal) should gain 25 to 35 lbs.; those with a BMI lower than 18.5 (underweight) should gain 28 to 40 lbs.; women with a BMI of 25 to 29.9 (overweight) should gain 15 to 25 pounds; and women with a BMI higher than 30 (obese) should limit weight gain to 11 to 20 lbs.