Comparing Old and New GDM Criteria: Caution Urged

New and older criteria for the diagnosis of GDM are associated with similar rates of cesarean delivery, shoulder dystocia, and infants who are large for gestational age.…

Katrien Benhalima, MD, from UZ Gasthuisberg in Leuven, Belgium, reported at IDF that, however, women diagnosed with GDM under the new criteria, proposed by the International Association of Diabetes and Pregnancy Study Groups (IADPSG), are more likely to be younger and multiparous than women diagnosed under the older criteria.

Boyd Metzger, MD, from Northwestern University Feinberg School of Medicine in Chicago, Illinois, warned that outcomes resulting from the new diagnostic criteria, which have been endorsed by the American Diabetes Association but not by the American College of Obstetricians and Gynecologists, should not be compared with outcomes resulting from older diagnostic criteria, He chaired the session and was a member of the IADPSG guidelines writing group.

According to Dr. Metzger, women diagnosed with GDM under the older (Carpenter–Coustan) criteria were treated appropriately, whereas those classified as having “normal” glucose tolerance test results were not treated. Under the new diagnostic criteria, that normal group would be diagnosed with GDM and treated, making a comparison of these 2 groups unfair.

“You cannot take an untreated and treated group and compare their outcomes,” Dr. Metzger said. “But you can compare them to those with normal glucose tolerance.”

Dr. Benhalima and colleagues retrospectively analyzed 6727 screenings for GDM conducted from 2005 to 2010. The mean age of the patients was 31 years and the mean body mass index was 23.7 kg/m²; 31% of the cohort was overweight and was 8% obese.

The researchers found that under the old criteria, 222 women were diagnosed with GDM (3.3%). Under the new criteria, 382 would have been diagnosed with GDM (5.7%), a relative increase in prevalence of 72%.

“Under the new IADPSG criteria, the threshold for the fasting and 2-hour [oral glucose tolerance test] is slightly lower than under the Carpenter-Coustan criteria, but the main difference is that only 1 abnormal value is enough for diagnosis under the new criteria,” Dr. Benhalima explained. Under the old criteria, at least 2 abnormal values were necessary for a diagnosis of GDM.

Of the 382 women diagnosed with GDM under the new criteria, 160 would have been classified as having normal glucose tolerance under the old criteria, she said.

Characteristics of the women diagnosed under the new and old criteria that are significantly different include age (31.6 vs. 33.3 years) and being black or another minority (19.7% vs. 17.4%).

Similarly, women diagnosed under the new criteria were more likely to be multiparous than those diagnosed under the old criteria (25.5% vs. 20.6%). These rates are significantly higher than those in women with normal glucose tolerance under both criteria (16.3%, P = .003).

In women classified as having normal glucose tolerance under both criteria, the incidence of cesarean delivery was 23%, which is significantly lower (P =.001) than in women with GDM diagnosed under either the old (32.4%) or new criteria (30.5%), Dr. Benhalima said.

In addition, the incidence of infants large for gestational age was slightly higher in women diagnosed with GDM under the old than under the new criteria (13.8% vs. 10.8%). Although this difference was not statistically significant, both rates differed significantly from rate of infants large for gestational age born to women with normal glucose tolerance under both criteria (1.4%; P = .007).

Dr. Metzger said that the IADPSG’s proposed new criteria are intended to affect treatment and outcomes; however, to date no treatment trials have been done using the new diagnostic criteria.

Many North American specialists are awaiting next year’s National Institutes of Health consensus conference on diagnosing GDM. The World Health Organization is expected to announce its position on this issue before that time.

Several recent studies guided by glucose values similar to the IADPSG’s criteria showed an expansion of the GDM diagnosis. Such cases were successfully treated with diet alone, he said.

“Expanding the population does increase the numbers,” Dr. Metzger said, “but it’s not going to have the same impact — I don’t think — on the number of people needing pharmacological treatment.”

International Diabetes Federation (IDF) World Diabetes Congress 2011, Abstract O-0394, Presented December 5, 2011