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Gestational Diabetes Diagnoses to Increase by 12%

Nov 21, 2012

The new threshold for the diagnosis of gestational diabetes may overwhelm the healthcare system….

Three articles published in two 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.


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.

Since the 1970s, GDM in the United States has been diagnosed through a 2-step process, starting with a 50 g glucose challenge test. 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.

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