Expert Commentary

The One Step test: The better diagnostic approach for gestational diabetes mellitus

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It is time for the United States to reconsider its guidelines for screening for GDM



Gestational diabetes mellitus (GDM) generally is defined as any degree of glucose intolerance with onset or first recognition during pregnancy.1-14 The best approach and exact criteria to use for GDM screening and diagnosis are under worldwide debate. In TABLE 1 we present just some of the many differing suggestions by varying organizations.2,7-9,11,12,15-17 The American College of Obstetricians and Gynecologists, for instance, suggests a Two Step approach to diagnosis.15 We will make the argument in this article, however, that diagnosis should be defined universally as an abnormal result with the One Step 75-g glucose testing, as adopted by the World Health Organization, International Federation of Gynecology and Obstetrics, and others. Approximately 8% of all pregnancies are complicated by GDM by the One Step test in the United States.18-22 The prevalence may range from 1% to 14% of all pregnancies, depending on the population studied and the diagnostic tests employed.1,19

Diagnostic options

Different methods for screening and diagnosis of GDM have been proposed by international societies; there is controversy regarding the diagnosis of GDM by either the One Step or the Two Step approach.6

The One Step approach includes an oral glucose tolerance test with a 75-g glucose load with measurement of plasma glucose concentration at fasting state and 1 hour and 2 hours post–glucose administration. A positive result for the One Step approach is defined as at least 1 measurement higher than 92, 180, or 153 mg/dL at fasting, 1 hour, or 2 hours, respectively.

The Two Step approach includes a nonfasting oral 50-g glucose load, with a glucose blood measurement 1 hour later. A positive screening, defined often as a blood glucose value higher than 135 mg/dL (range, 130 to 140 mg/dL), is followed by a diagnostic test with a 100-g glucose load with measurements at fasting and 1, 2, and 3 hours post–glucose administration. A positive diagnostic test is defined as 2 measurements higher than the target value.

Why we support the One Step test

There are several reasons to prefer the One Step approach for the diagnosis of GDM, compared with the Two Step approach.

Women testing negative for GDM with Two Step still experience complications pregnancy. Women who test positive for GDM with the One Step test, but negative with the Two Step test, despite having therefore a milder degree of glucose intolerance, do have a higher risk of experiencing several complications.23 For the mother, these complications include gestational hypertension, preeclampsia, and cesarean delivery. The baby also can experience problems at birth (TABLE 2).23 Therefore, women who test positive for GDM with the One Step test deserve to be diagnosed with and treated for the condition, as not only are they at risk for these complications but also treatment of the GDM decreases the incidence of these complications.18,19

There is indeed an increased GDM diagnosis rate with the One Step (about 8%) compared with the Two Step test (about 4%). Nonetheless, this increase is mild and nonsignificant in the meta-analysis of randomized controlled trials (RCTs),18,19 is less than the 18% difference in diagnosis rate previously hypothesized, is consistent with the increased diabetes/prediabetes rates in the general population, and is linked to the increasing incidence of obesity and insulin resistance.

Overall test adherence is better. Five percent to 15% of patients, depending on the study, are not adherent with taking the second part of the Two Step test. Women indeed prefer the One Step approach; the second step in the Two Step approach may be a burden.

Less costly. The One Step process is cost-effective when postpregnancy diabetes mellitus prevention is considered.

Better maternal and perinatal outcomes. Probably the most important and convincing reason the One Step test should be used is that meta-analysis of the 4 RCTs comparing the approaches (including 2 US trials) shows that diagnosing and treating mild GDM as per the One Step approach, compared with screening and treating using the Two Step approach, is associated with increased incidence of GDM (8% vs 4%) and with better maternal and perinatal outcomes.13,18,19 In fact, the One Step approach is associated with significant reductions in: large for gestational age (56%), admission to neonatal intensive care unit (51%), and neonatal hypoglycemia (48%). Tests of heterogeneity in the meta-analysis and of quality all pointed to better outcomes in the One Step test group.13,19

The need for a second step in the Two Step approach delays diagnosis and treatment. The One Step approach is associated with an increase in GDM test adherence and earlier diagnosis,13 which is another reason for better outcomes with the One Step approach. In the presence of risk factors, such as prior GDM, prior macrosomia, advanced maternal age, multiple gestations, and others, the One Step test should be done at the first prenatal visit.

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