David has blogged in the past about the diagnosis of gestational diabetes mellitus (GDM). In July 2012 he discussed a debate that was underway among experts regarding newly proposed diagnostic guidelines.
Just to recapitulate the debate, for at least 10 years we have been diagnosing GDM with a two-step process.
- First, there is a screening test performed by giving a non-fasting woman a 50-gram dose of glucose and then measuring her serum glucose 1 hr later. If the woman's glucose concentrations were higher than expected in that screen, then she went on to a diagnostic test.
- For the diagnostic test, a fasting patient is given 100-gram of glucose and then serum glucose concentrations are measured at 0, 1, 2 and 3 hours.
In 2010, the International Association of Diabetes in Pregnancy Study Groups (IADPSG) made recommendations for glucose tolerance testing in pregnancy based on the results of a study called HAPO (Hyperglycemia and Adverse Pregnancy Outcomes). That study clearly demonstrated that the risks of adverse maternal and fetal outcomes continually increase as maternal glucose concentrations increase. In 2011, the American Diabetes Association adopted these new diagnostic criteria. In the new diagnostic approach, a 75-gram load is given to fasting women and blood is collected at 1 and 2 hours. However, also in 2011, the American College of Obstetricians and Gynecologists issued a statement indicating:
"Diagnosis of GDM based on the one-step screening and diagnosis test outlined in the International Association of Diabetes in Pregnancy Study Group guidelines is not recommended at this time because there is no evidence that diagnosis using these criteria leads to clinically significant improvements in maternal or newborn outcomes and it would lead to a significant increase in health care costs."
This is not surprising coming from ACOG. Their position is always to ask for evidence that new protocols: a) positively affect outcomes; and, b) do not harm the mother or infant. However, this division between the ADA and ACOG left everyone with the debate that David discussed in July 2012.
In March 2013, the National Institutes of Health (NIH) held a consensus development conference which convened an independent panel of health professionals and public representatives. During the conference invited experts presented and discussed current scientific data.
They addressed the following questions:
- What are the current approaches for GDM, what are the glycemic thresholds for each approach, and how were they chosen?
- What are the effects of various screening/diagnostic approaches for patients, providers, and U.S. healthcare systems?
- In the absence of treatment, how do the outcomes of mothers and their offspring compare with those who do not?
- Does treatment modify the health outcomes of mothers and their offspring?
- What are the harms of treating?
- Given all of the above, what diagnostic approach(es) for gestational diabetes mellitus should be recommended, if any?
- What are the key research gaps in the diagnostic approach of gestational diabetes mellitus?
The committee felt that a one-step approach would, in many ways, be advantageous over the two-step approach. First, the current two-step approach is not used other than during pregnancy and is largely restricted to the United States. Second, there would be value in a consistent diagnostic approach across an individual's lifespan, within the United States, and during pregnancy around the world. This would allow better standardization of best practices and comparability of research outcomes. The one-step approach would also allow a diagnosis to be made within a single healthcare visit.
The committee felt that there is good evidence that increasing glucose concentrations during pregnancy are associated with greater maternal and perinatal morbidities. They also state that there is evidence that treatment of women with GDM—diagnosed either by the one-step or two-step approach—may improve some outcomes. However, the new one-step approach, as proposed by the IADPSG, is anticipated to increase the diagnosis of GDM by 2-3 fold, to a prevalence of approximately 15-20%. Because it is unclear if these women will benefit from treatment and these additional diagnoses will increase health care costs, the consensus committee concluded that the old two-step method for diagnosis should be retained.
"…at present, the panel believes that there is not sufficient evidence to adopt a one-step approach, such as that proposed by the IADPSG. The panel is particularly concerned about the adoption of new criteria that would increase the prevalence of GDM, and the corresponding costs and interventions, without clear demonstration of improvements in the most clinically important health and patient-centered outcomes. Thus, the panel recommends that the two-step approach be continued. However, given the potential benefits of a one-step approach, resolution of the uncertainties associated with its use would warrant reconsideration of this conclusion."
The panel went on to identify 9 areas of research that are needed including outcomes and cost benefit ratio studies. This certainly lays the groundwork for years of future studies. In the meantime, there seems to be a great deal of support for maintaining the two-step approach for diagnosis of GDM.