One-step GDM diagnosis: Research moves closer




Data are accumulating that lend more support to a one-step approach for diagnosing gestational diabetes mellitus in the United States.

The American College of Obstetricians and Gynecologists now acknowledges this approach as an option, yet “tremendous controversy persists,” according to Mark Landon, MD.

“In the U.S., we continue to be the principal purveyors of a two-step method with a 100-g [oral glucose tolerance test] diagnostic approach, which is in contrast to much of the rest of the world,” he said the biennial meeting of the Diabetes in Pregnancy Study Group of North America.

“At this time, if we’re going to [turn nationally] to the one-step approach, we have to lower the cost of diagnosis and treatment, and we may need some upwards adjustments in the [International Association of Diabetes and Pregnancy Study Groups] criteria in order to achieve consensus,” said Dr. Landon, professor and chair of the department of obstetrics and gynecology at Ohio State University, Columbus.

The International Association of Diabetes in Pregnancy Study Groups (IADPSG) created a stir in the American obstetrics community when it recommended in 2010 that a universal 75-g, 2-hour oral glucose tolerance test (OGTT) be performed during pregnancy and that gestational diabetes mellitus (GDM) be diagnosed when any single measurement threshold – a fasting value of 92 mg/dL, a 1-hour value of 180 mg/dL, or a 2-hour value of 153 mg/dL – is met or exceeded (Diabetes Care 2010 Mar; 33[3]:676-82).

The consensus group made its recommendation based largely on published associations of maternal glycemia with perinatal and long-term outcomes in offspring. Chief among the studies was the landmark Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study, which found continuous linear relationships between maternal glucose levels – including levels that had been viewed as normal – and adverse fetal outcomes such as high fetal birth weight, cord-blood serum C-peptide level (an index of fetal beta-cell function and fetal hyperinsulinemia), and clinical neonatal hypoglycemia. Maternal glucose tolerance was measured in the study with the 75-g 2-hour OGTT.

The IADPSG chose its cut-off points to convey an odds ratio for adverse outcomes of 1.75. But use of the criteria meant that 16%-18% of pregnant women in the United States would be identified as having GDM – a doubling, at least.

Dr. Mark B. Landon Courtesy Ohio State University
Dr. Mark B. Landon

In 2013, a National Institute of Child Health and Human Development Consensus Development Conference recommended against adoption of the new criteria, citing uncertainties regarding the benefits of treating so many additional cases of GDM, as well as the costs and additional burden on patients, providers, and the health care system.

In an updated Practice Bulletin on GDM, ACOG recommends that the suggested changes be studied “before they are proposed at a national level.” But ACOG noted that “individual practices and institutions may choose to use the IADPSG’s recommendation, if appropriate, for the population they serve” (Obstet Gynecol. 2017;130[1]:e17-37).

Since the IADPSG proposal came out, Dr. Landon said, at least a half-dozen published studies have attempted to clarify the additional benefit of their proposed criteria, analyzing the risk of adverse maternal and fetal outcomes in women who are diagnosed using IADPSG criteria and not treated, versus those with a normal glucose tolerance test. In these analyses, researchers have excluded women who would also meet usual diagnostic criteria, such as the Carpenter-Coustan criteria, in order to hone in on those with the mildest levels of GDM – the new diagnoses.

Research published “in the last 5-6 years has almost exclusively shown that, in using the IADPSG criteria, and excluding other usual criteria, you see graded, increased frequencies in large babies, preeclampsia, [neonatal] hypoglycemia” and other adverse outcomes, Dr. Landon said. “I know of only one study that refutes these associations.”

A secondary analysis of HAPO study data, for instance, grouped women into three categories: those with no GDM, GDM based on traditional Carpenter-Coustan criteria, and GDM based on IADPSG criteria but not the Carpenter-Coustan thresholds. A 3-hour OGTT result was not used in this analysis since the HAPO study did not collect this.

Compared with cases with no GDM, those with GDM based on IADPSG criteria (but not the Carpenter-Coustan criteria) were nearly twice as likely to have birth weights above the 90th percentile, newborn percentage fat over the 90th percentile, and preeclampsia, for instance (Diabetes Care 2016;39[12];2204-10).

Other researchers are trying to tease apart risk levels according to thresholds that differ slightly from traditional criteria. A retrospective cohort study from Kaiser Permanente Southern California, for instance, chose two strata of women whose GDM was in the lower levels of the IADPSG-defined spectrum for glucose intolerance and found that, in those with the lesser degree of hyperglycemia, only birth weight and large-for-gestational-age was significantly greater than in women with no GDM (Obstet Gynecol. 2015;126[1]:67-73).

“This study is interesting because it raises the question of whether there might be differential treatment effects based on the level of hyperglycemia within the IADPSG category,” Dr. Landon said.

Dr. Landon served as the principal investigator of a large national, randomized controlled trial that showed a reduction in the risk of fetal overgrowth, shoulder dystocia, cesarean delivery, and hypertensive disorders in women who were treated for mild gestational diabetes (N Engl J Med. 2009;361:1339-48). But this study defined mild gestational diabetes according to the Carpenter-Coustan criteria.

“What about the women who meet the [even lower thresholds] of the IADPSG criteria? One would expect that the treatment benefit would not be as great, but will they still benefit from treatment? To date, this is simply unknown,” he said in an interview.

Research in the last 5 years has also begun to look at the financial implications of the IADPSG criteria and strategies for reducing the cost of implementation. Dr. Landon noted that investigators in Brazil, for instance, have determined that an alternative strategy of using a fasting plasma glucose value of 92 mg/gL or greater to rule in GDM, and a fasting value of 80 mg/dL or less to rule out GDM, eliminates the need for 61% of oral glucose challenges and has 96.9% sensitivity for diagnosing GDM (Diabetes Res Clin Pract. 2015 May;108[2]:288-95).

Dr. Landon reported having no relevant financial disclosures.
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