Gestational Diabetes May Become More Frequent Diagnosis

Jenni Laidman

November 12, 2012

Three articles published in 2 obstetrics journals challenge the wisdom of immediately lowering the threshold for diagnosis of gestational diabetes mellitus (GDM), warning that evidence for benefit is inadequate and could result in more labor induction, more cesarean deliveries, and a surge in new patients who may overwhelm an already overburdened primary healthcare system.

The articles were published online in late October and early November to coincide with the National Institutes for Health Consensus Development Conference on proposed changes in the diagnostic criteria for GDM. Hurricane Sandy forced the rescheduling of the conference to next year.

Although the authors acknowledge that research, especially the 2008 Hyperglycemia and Adverse Pregnancy Outcomes (HAPO) study, has shown a relationship between subclinical hyperglycemia and fetal macrosomia, as well as clinical neonatal hypoglycemia, they are less convinced that the benefits of treating smaller glucose abnormalities are proven.

A lower GDM threshold would have a certain effect on the healthcare system, with the number of GDM cases rising from 4% to 6% of pregnancies to 17.8%, according to Oded Langer, MD, PhD, and colleagues, in their article published online October 19 in Obstetrics & Gynecology. Dr. Langer was affiliated with Cookeville Regional Medical Center in Tennessee when he wrote the article and is currently professor of obstetrics & gynecology at Columbia University.

The system is not prepared for the rush of new patients, according to the authors of the second article, published online November 2 in American Journal of Obstetrics & Gynecology.

"Although it is desirable from a public health standpoint to potentially prevent downstream consequences for women with milder forms of GDM and their babies, it also is prudent to be prepared to accommodate the onslaught of new patients such a change in current diagnostic and screening practices is liable to entail," E. Albert Reece, MD, PhD, MBA, vice president for medical affairs, University of Maryland John Z. and Akiko K. Bowers Distinguished Professor of Obstetrics Gynecology and Reproductive Sciences, and dean, University of Maryland School of Medicine, Baltimore, Maryland, and Thomas Moore, MD, professor and chairman, Department of Reproductive Medicine, University of California, San Diego, write. "More importantly, we also must be able to ensure that we know more precisely the level of care these women will require and whether the prescribed care will produce the improved outcomes we — and they — desire. Otherwise, we may find ourselves plunging headlong into a workforce shortage abyss from which it will be difficult to escape."

Although the American Congress of Obstetricians and Gynecologists has not endorsed the suggested diagnostic criteria, the American Diabetes Association has accepted the new GDM standards.

"We need a uniform way to define GDM to help with comparisons, epidemiology, etc," M. Sue Kirkman, MD, senior vice president, Medical Affairs and Community Information, American Diabetes Association, wrote in an email to Medscape Medical News. Dr. Kirkman was not involved with any of these articles. "There is significantly more evidence for the new criteria than for the old ones that some seem to feel are some sort of gold standard," she added.

Since the 1970s, GDM in the United States has been diagnosed through a 2-step process, starting with a 50 g glucose challenge test, Dr. Reece and Dr. Moore write. Those patients whose plasma glucose is 140 mg/dL or higher in the challenge are given a 3-hour, 100-g oral glucose tolerance test (OGTT), with plasma glucose concentration measured 2 to 3 hours later. GDM is diagnosed if a pregnant woman exceeds the current OGTT threshold of 180 mg/dL or more at 1 hour, 155 mg/dL or more at 2 hours, and 140 mg/dL or more at 3 hours. Two or more positive tests results in a GDM diagnosis.

As evidence mounted for adverse pregnancy outcomes at subclinical levels of hyperglycemia, suggestions to change the threshold emerged, with the International Association of Diabetes and Pregnancy Study Groups in 2010 recommending eliminating the challenge stage and moving to a 1-step, 75 g GTT with lower thresholds for diagnosis, based on a single abnormal value. The thresholds are fasting glucose levels of 92 mg/dL or more, 1-hour plasma glucose levels of 180 mg/dL or more, and 2-hour plasma glucose levels of 152 mg/dL or more. Outside of the United States, the 1-step 75 g OGTT with a single positive result diagnostic of GDM is a common standard.

A major influence in this recommendation was the HAPO study, which used a 1-step 75 g OGTT screen in a large cohort and identified an association between adverse outcomes and maternal glucose levels below the diagnostic range.

However, many in the obstetrical community object that simply changing diagnostic criteria is no guarantee of improved outcome.

"The main issue is we have not yet proven that diagnosing in this way improves outcome," George Saade, MD, chief, Division of Maternal-Fetal Medicine, University of Texas Medical Branch, Galveston, told Medscape Medical News. Dr. Saade was not involved in any of these articles. "Data shows association between this level of hyperglycemia and certain outcomes we don't like, but that doesn't translate to saying we should screen and detect because we can modify and prevent this outcome. We don't have that data. We need data showing that modifying the threshold will lead us to do something different and improve outcomes, but not cause harm."

Donald R. Coustan, MD, professor of obstetrics and gynecology, Warren Alpert Medical School of Brown University, Providence, Rhode Island, who favors the new guidelines, told Medscape Medical News that the data are there. Two studies showed that intervening at lower levels of hyperglycemia led to a significant reduction in big infants and preeclampsia. "To me, that underscores the fact that identifying and treating these patients can reduce adverse outcomes," Dr. Coustan said. For most patients in these studies, diet was the only intervention. Eight percent of the women in 1 study and 20% in the other needed insulin.

"In most of the world, they are already dealing with people already that low," Dr. Coustan said. "What it boils down to is, How much do we have to know before we decide to make the change?"

Still, he agrees that the rising medical needs created by a larger group of patients with GDM could overwhelm the system. "What are we going to do with this influx of patients that's going to swamp us? I think that is a realistic issue. I think it's something we're going have to deal with, just as we're currently having to deal with the epidemic of diabetes."

However, those reluctant to change the guidelines worry that dealing with low-level GDM could result in more significant interventions.

"When a woman is diagnosed, we have to deliver more care," Kjersti Aagaard, MD, PhD, associate professor of obstetrics and gynecology at Baylor College of Medicine in Houston, Texas, who was not involved in any of the studies told Medscape Medical News. "Because we have a higher population [with a GDM diagnosis], we may have a higher cesarean section rate."

In the second article from the American Journal of Obstetrics & Gynecology, published online October 26, Gerald H.A. Visser, MD, from the Department of Obstetrics, and Harold W. de Valk, MD, PhD, from the Department of Internal Medicine, University Medical Center, Utrecht, the Netherlands, write that the proposed one-time test has poor reproducibility and that it will not solve a large portion of the fetal macrosomia problem. Further, although GDM is related to childhood obesity, the stronger relationship is with maternal obesity.

"We need to press the pause button," Dr. Langer writes in Obstetrics & Gynecology. "Rather than moving forward to universal adoption of diagnostic criteria that have been tested only by an elaborate retrospective 'thought experiment' using data from the [HAPO] study, we have the moral responsibility to encourage empirical prospective research that will maximize certainty, consistency, and predictability of the clinical and social effects of this change in GDM diagnosis."

Neither the authors nor the commentators have disclosed any relevant financial relationships.

Am J Obstet Gynecol. Published online October 26 and November 2, 2012. Visser and de Valk abstract Reece and Moore abstract

 Obstet Gynecol. 2012;120:989-1256 Abstract