The gestational diabetes mellitus debate continues

Discussion_icon_noshadowI have just returned from the annual meeting of the AACC where I attended a very interesting debate on the diagnosis of gestational diabetes mellitus (GDM). I've written about the current controversy in diagnosing GDM before and you can read about those here and here. Basically, the controversy boils down to one issue: should recently recommended criteria for identifying pregnant women with GDM be globally implemented or not? 

Arguing for that position was Dr. Donald Coustan from Brown University and regional principal investigator for North America of the Hyperglycemia and Adverse Pregnancy Outcomes (HAPO) study. He correctly pointed out that lack of a universal testing strategy when screening for GDM makes it impossible to compare clinical studies on GDM. He reviewed how the new IADPSG glucose cutoffs came into being (they were based on risk of adverse infant outcomes) that he advocates referring to as the ADA criteria because the ADA is recommending the use of the new testing method.

Arguing against the use of the ADA criteria was Dr. Sean Blackwell from the University of Texas Health Science Center at Houston, TX. He agreed with several of Dr. Coustan points. Among them that:

  1. The HAPO study was well conducted.
  2. There was a positive association between glucose concentration and adverse infant and maternal outcomes at lower glucose cutoffs than are currently used to diagnose GDM.
  3. There is benefit in having a single, universal screening test for GDM.
  4. There is evidence that, as currently defined, treatment of GDM improves outcomes.

He had two major problems with use of the new ADA criteria. The first was that its use would double the number of women diagnosed with GDM (from about 7% to 16%). The second was that the HAPO study was an observational study, not a treatment trial and, as such, there is no evidence that treating these additional women for GDM is effective or safe.

Dr. Coustan argued that the increase in the number of GDM diagnoses is not surprising given that, in the US, 31% of adult US women have either diabetes or pre-diabetes. He also argued that the Australian Carbohydrate Intolerance Study of Pregnant Women (ACHOIS) study demonstrated that treatment of women with mild GDM reduced adverse outcomes such as large for gestational age newborns, macrosomia, and preeclampsia.

Dr. Blackwell pointed out that most of the additional 10% of women that would be diagnosed with GDM under the ADA criteria would, by definition, have "milder" GDM and would only require nutritional modification and glucose monitoring rather than drugs to control their GDM. These women would have glucose control similar to those of obese women without diabetes. Further, he added that several studies in obese women without diabetes have failed to demonstrate that nutritional interventions have any impact on any infant health outcome.

The moderator of this debate was my co-blogger, Ann Gronowski. Prior to its start, she polled the audience of (mostly) laboratorians to see which testing strategy they currently offered at their institutions. Most indicated they offered the current ACOG criteria (advocated by Dr. Blackwell). At the end of the debate, the audience was asked if they would support switching to the new, ADA criteria. The majority response was "yes." Dr. Coustan argued his points effectively.

It's my belief that the evidence, while not complete, is strong enough to support widespread adoption of the ADA criteria when screening for and diagnosing GDM.

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