New criteria for gestational diabetes diagnoses
Gestational diabetes mellitus (GDM), more commonly referred to as gestational diabetes, is an inability of the body to manage blood sugar levels during pregnancy in women who were not diabetic prior to their pregnancy. The condition can result in harm or even death to the developing fetus. According to a new study by Italian researchers, the use of more stringent criteria for diagnosing gestational diabetes is associated with a 137% increase in prevalence (number of cases). The study was presented at the International Diabetes Federation World Diabetes Congress 2011 in Dubai, which runs from December 4-8. The new criteria, which was proposed by the International Association of Diabetes and Pregnancy Study Groups (IADPSG), was recently adopted recently in Italy.
The new criteria necessitate a diagnosis of gestational diabetes after a single abnormal fasting plasma glucose measurement of 92 to 126 mg/dL at the first prenatal visit or, if the initial test is normal, an abnormal oral glucose tolerance test at 24 to 28 weeks of pregnancy. If the fasting plasma glucose is 92 mg/dL or greater, gestational diabetes is diagnosed when the 1-hour value is 180 mg/dL or greater or when the 2-hour value is 153 mg/dL or greater.
Emilia Lacaria and her colleagues at the University of Pisa in Italy, analyzed 660 pregnant women who were being evaluated for gestational diabetes using the new criteria, and compared them with a historic cohort (previous study group) that had been evaluated using the old Carpenter–Coustan criteria. The mean age of the women was 33 years, 18.5% had a family history of diabetes, and 58% were primiparous (first pregnancy). An early diagnosis of gestational diabetes was made in 18 women; the other 642 women underwent an oral glucose tolerance test; this yielded a diagnosis of gestational diabetes in another 118 women and normal glucose tolerance in the rest (79.4%). In total, 136 (20.6%) women were diagnosed with gestational diabetes (13.2% after early evaluation and 88.8% after an oral glucose tolerance test). When the researchers compared their study group to a historic cohort of 3950 women diagnosed using the older criteria, the new criteria were associated with a 136.8% increase in prevalence (20.6% vs. 8.7%).
After analyzing the data from the historical cohort and including all subjects (6.7%) were classified as having impaired glucose tolerance in the gestational diabetes group, the difference was less apparent (20.6% vs. 15.4%); however, a 34% difference still remained. The dramatic increase in gestational diabetes diagnosis seen with the proposed IADPSG criteria has been the subject of much discussion; however, it is important to note that using old data as a comparator is inherently flawed, said Boyd Metzger, MD, from Northwestern University Feinberg School of Medicine in Chicago, Illinois, who chaired the session and was a member of the IADPSG guidelines writing group. He noted, "There's been a continuous rise in overweight and obesity around the globe, and there are several papers showing that when using exactly the same standardized approach, the incidence of gestational diabetes has gone up 40% to 50%... There's been a continuously moving background, so it's very hard retrospectively to compare." Dr. Metzger explained that many diabetes experts in the U.S. are waiting for next year's National Institutes of Health consensus conference on diagnosing gestational diabetes to make a decision regarding the new criteria. Prior to that conference, the World Health Organization (WHO) is expected to announce its position. The new criteria have been endorsed by the American Diabetes Association (ADA); however, to date, they have not been approved by the American College of Obstetricians and Gynecologists (ACOG).
Dr. Metzger is of the opinion that the striking increase in diagnosis of gestational diabetes with the new criteria is due to the fact that now only one abnormal test is required. Previous criteria required two abnormal oral glucose tolerance tests. He explained, "There have been dozens of papers written in the past 20 years pointing out that people who had one abnormal test value and who were called "normal" had a lot of the outcomes that are similar to those who were diagnosed."