Diabetes Dateline
Winter 2008

Research News

Study Finds Increased Risk of Fetal Health Problems at Lower Maternal Blood Glucose Levels

Women with gestational diabetes mellitus (GDM) and their unborn babies may be at greater risk for health problems at lower maternal blood glucose levels than previously thought, according to results of the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study. The results of the study, which was supported by the National Institutes of Health and the American Diabetes Association (ADA), were announced at the ADA’s 67th Annual Scientific Sessions in Chicago.

“We found that the risk of having a large baby, a first-time Cesarean delivery, low blood glucose levels in the newborn requiring treatment, and high blood insulin levels in the baby that may signal problems ahead all increased as the mother’s blood glucose level during pregnancy increased,” said Boyd E. Metzger, M.D., principal investigator of the study and professor of medicine in the division of endocrinology at Northwestern University’s Feinberg School of Medicine. “These relationships were continuous over the entire range of blood glucose levels found in over 23,000 pregnancies, even in ranges previously considered to be within the normal range for pregnant women.”

GDM, defined as high blood glucose levels first discovered during pregnancy, affects about 135,000, or 4 percent, of pregnancies annually in the United States. Women with GDM receive treatment—meal planning, physical activity, and, if needed, insulin injections—to keep blood glucose levels on target during pregnancy.

GDM usually disappears after pregnancy, but women who have had it are at high risk for developing it in subsequent pregnancies—along with type 2 diabetes later in life. In addition, children of mothers with GDM may be at increased risk for obesity during childhood and type 2 diabetes in adulthood.

The HAPO study, conducted in nine countries over 7 years, examined the relationship in 23,325 women between blood glucose levels during the third trimester of pregnancy and the risk of adverse outcomes in the mother and fetus. At about week 28 of the pregnancy, each woman in the study provided three blood samples: a morning fasting blood glucose and, in the oral glucose tolerance test, one sample an hour after drinking a beverage containing 75 grams of glucose and another sample a second hour later. Outcomes were analyzed following delivery.

“We found major independent effects of the mother’s blood glucose level on each of the outcomes—the size of the baby, the need for a first Cesarean delivery, low blood glucose requiring treatment, and high insulin levels in the newborn,” said Metzger.

The study findings leave several questions open for discussion and resolution, including which blood glucose levels should be considered above normal and which type of blood glucose test is best for diagnosis. A conference involving health care providers, patients, and third-party payers to translate study results into clinical recommendations is planned for June 11 to 13, 2008, in Pasadena, CA, immediately following the ADA meeting in San Francisco.

The National Diabetes Information Clearinghouse has easy-to-read booklets in English and Spanish about gestational diabetes. The booklets are available at www.diabetes.niddk.nih.gov/dm/pubs/gestational.

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NIH Publication No. 08–4562
March 2008