POINT: Preventing adverse outcomes in newborns is imperative.
In March 2013, an independent panel at a National Institutes of Health consensus development conference recommended against adopting the one-step approach to diagnosis of gestational diabetes mellitus (GDM) that was recommended in 2008 by the International Association of Diabetes and Pregnancy Study Groups (IADPSG) and adopted by the American Diabetes Association, the World Health Organization, and organizations in other countries. The NIH panel voiced concerns about costs and interventions that would accompany an increased prevalence of GDM, as well as uncertainties about the benefits of identifying and treating so many additional new cases of GDM.
The panel’s recommendation is inconsistent with available data. There is more than sufficient evidence that the one-step approach should be used worldwide – without waiting for more research.
Dr. Donald R. Coustan
The study on which the IADPSG criteria were based – the Hyperglycemia and Adverse Pregnancy Outcomes (HAPO) Study (N. Engl. J. Med. 2008;358:1991-2002) – involved more than 23,000 pregnancies in nine different countries. All of the adverse pregnancy outcomes evaluated were related directly and significantly, and in a continuous fashion, to glucose concentrations at the fasting, 1-hour, and 2-hour points in a single 75-g, 2-hour oral glucose tolerance test (OGTT).
The IADPSG recommended that GDM be diagnosed when one or more of the plasma glucose values were met or exceeded: fasting, 92 mg/dL; 1-hour, 180 mg/dL; 2-hour, 153 mg/dL. According to the HAPO study data, patients with GDM have an approximate doubling of the likelihood of a birth weight above the 90th percentile compared to those without GDM, as well as a near-tripling of the likelihood of fetal hyperinsulinemia, twice the likelihood of preeclampsia, and a 50% increase in primary cesarean section, among other increased complication rates (Diabetes Care 2010;33:676-82).
The IADPSG diagnostic criteria are based on a predictive value of a 1.75 odds ratio above the mean for large for gestational age (LGA), neonatal body fat greater than 90th percentile, and cord blood hyperinsulinemia. This is equivalent to a doubling in the likelihood of these outcomes, because the 1.75 odds ratio is compared to the mean rather than to everyone without GDM.
HAPO was indeed an observational study, but we have solid data from other randomized trials demonstrating that intervention for mild GDM will prevent excess adverse outcomes.
In one of two recent randomized single-blinded trials on identifying and treating GDM, mild GDM was defined as a 2-hour, 75-g OGTT value between 140 and 198 mg/dL with a fasting plasma glucose value less than 140 mg/dL (mean, 86 mg/dL) – diagnostic criteria that, if anything, are lower than the IADPSG criteria. Patients randomized for intervention had a 66% reduction in "serious complications." Macrosomia was reduced by 50%, and preeclampsia by 30%. The cesarean rate was unchanged between the 1,000 women in the intervention and routine care groups (N. Engl. J. Med. 2005:352:2477-8).
In the second study of 958 women, identification and treatment lowered by half the rates of macrosomia, preeclampsia, and shoulder dystocia. There were other significant reductions in complications, and no difference in the rate of small-for-gestational-age infants (N. Engl. J. Med. 2009;361:1339-48). The criteria used to define mild GDM in this study meet the lower of two alternative sets of criteria recommended by the American College of Obstetricians and Gynecologists, but with a normal fasting plasma glucose concentration of 95 mg/dL or less.
Critics of the recommendations in the United States who say it is unreasonable and too expensive for such a large proportion of pregnant women to be identified as having a disease – 16%-18% in the HAPO population – need to look at the big picture.
Among women in the United States aged 18-44 years, 5% had diabetes and 26% had prediabetes from 2005 to 2008. Why, then, is 16%-18% called outrageously high, when the rate of prediabetes/diabetes outside of pregnancy is almost twice as high?
Undoubtedly, an increase in the number of mild GDM cases will increase costs – just as the broader epidemic of diabetes and prediabetes is increasing health care costs. Cost and resource issues are insufficient reasons, however, not to identify high-risk pregnancies in which adverse outcomes can be prevented with relatively simple interventions.
Indeed, we must develop more efficient ways to care for patients with GDM, but this is within our reach. We know from the trials of identifying and treating mild GDM that diet treatment is largely effective; only 8% and 20% women in these studies required insulin. This is reassuring. Group patient education may be helpful, and we have evidence that less frequent glucose monitoring – every second or third day, rather than daily – may be feasible.