Michelle Williams

Michelle Williams

Gestational diabetes: The diagnosis debate

August 9, 2013 — Gestational diabetes—diabetes that women develop while pregnant—can lead to serious health problems for both babies and mothers. Babies can be born too large or have birth injuries. Mothers can face greater risk of needing a cesarean delivery. For both mothers and babies, the risk of developing type 2 diabetes later in life can increase. But there’s a lack of clear evidence—and thus a lack of consensus—about the best way to test for and diagnose gestational diabetes. And much more could be done in terms of preventing the ailment in the first place.

Harvard School of Public Health’s Michelle Williams gave an overview of the controversies and challenges surrounding gestational diabetes at a summer Hot Topics lecture at the School on August 6, 2013.

Watch a video of the Hot Topics lecture

“Gestational diabetes is one of those conditions where we just can’t seem to decide how to define it and how we should screen for it,” said Williams, Stephen B. Kay Family Professor of Public Health and chair of the Department of Epidemiology. But the condition has been on the rise in recent years, in step with the worldwide rise in obesity. According to current estimates, 5%-7% of pregnant women in the U.S.—nearly a quarter of a million each year—develop gestational diabetes.

Pregnancy as “stress test”

The ailment is driven by the profound metabolic and physiologic changes that accompany pregnancy—changes that aid in the transfer of nutrients to the fetus but may cause adverse effects in some women. During pregnancy, estrogen and progesterone levels shoot up, as do cholesterol and triglyceride levels. “Good” (HDL) cholesterol goes down. Some women develop hyperglycemia—high blood sugar—which can be a transient problem or a precursor of gestational diabetes.

“You have this metabolic state that’s primed for oxidative stress,” Williams said. “If you add hyperglycemia to that, you can see we have a metabolic recipe for disaster.”

Recent studies have shed new light on the condition. The 2008 HAPO [Hyperglycemia and Adverse Pregnancy Outcomes] study showed that hyperglycemia with any degree of severity—even below the threshold of diagnosis for either gestational diabetes or type 2 diabetes—is associated with adverse pregnancy outcomes. Two other large studies—the 2005 Australian Carbohydrate Intolerance Study in Pregnant Women [ACHOIS] and the 2009 Maternal-Fetal Medicine Units Network [MFMUN-GDM] study—both showed that diagnosis and treatment of gestational diabetes improves maternal and fetal outcomes.

Diagnosis debate

But debate remains over what kind of test is best for diagnosing gestational diabetes, as well as what level of hyperglycemia actually indicates a problem. Current U.S. guidelines call for an initial screening and a follow-up diagnostic test, if necessary; many European and other countries use a one-step test that’s less burdensome for the patient and also more sensitive—which means that it typically results in higher rates of diagnosis. Were the U.S. to switch, the number of women diagnosed with gestational diabetes could double or even triple “overnight,” said Williams, raising concerns about costs and overwhelming the health system.

While costs and capacity are indeed a concern, Williams said experts should also be concerned by “the undue burden of a child developing in a metabolic toxic environment,” she said.

“So this is where we are,” she continued. “Do we address the concern that hyperglycemia at any degree is potentially harmful to the developing fetus? Or do we put our chips down on the side that we could be overdiagnosing gestational diabetes that’s of limited consequence to the developing fetus and that results in tripling the workload for the nutritional counselors and the reproductive endocrinologists and obstetricians who would be managing these pregnancies?”

Needed: research and prevention

More research is needed to determine whether or not the more sensitive screening and diagnostic approach truly provides a benefit to mothers and infants, Williams said. In the meantime, focusing on prevention would be wise. Armed with existing knowledge about a host of risk factors for gestational diabetes, such as obesity, advanced maternal age, family history of diabetes, and sedentary lifestyle, clinicians could emphasize more strongly to high-risk pregnant women the importance of a healthy diet, exercise, and adequate sleep—lifestyle habits that have all been associated in recent studies with reduced risk.

“Research gaps remain. Controversies exist,” said Williams. “But the health of women and children are in the balance.”

Karen Feldscher