One-step screening approach detected more gestational diabetes than two-step approach but did not improve clinical outcomes

A recent trial compared two approaches for gestational diabetes mellitus (GDM) screening. More than 20,000 women were randomized to either a single two-hour oral glucose tolerance test (OGTT) or a one-hour glucose challenge test followed by a three-hour OGTT on a second visit if the first test was positive. GDM was diagnosed in 16.5% and 8.5%, respectively, but there were no significant differences between groups in the other primary outcomes: large-for-gestational-age infant, a composite of adverse birth outcomes, gestational hypertension or preeclampsia, and primary cesarean section.

The study was published by the New England Journal of Medicine on March 11 and summarized in the March ACP Diabetes Monthly. The following commentary by Robert P. Kauffman, MD, was published in the ACP Journal Club section of Annals of Internal Medicine on Aug. 3.

There is no optimal test to diagnose type 2 DM or GDM. The diagnostic values for GDM screening and formal OGTT are not consistently defined, leaving clinicians to determine the best cut points. Moreover, the OGTT is problematic in pregnancy given its suboptimal reproducibility (approximately 75%) and dependence on several maternal physiologic factors when administered. The value of hemoglobin A1c measurement in pregnancy is affected by its limited ability to capture postprandial glucose excursions and pregnancy-associated accelerated red cell turnover.

The ScreenR2GDM trial by Hillier and colleagues compared 1-step and 2-step screening approaches for diagnosing GDM and assessed associated clinical outcomes. 1- and 2-step approaches had substantial differences in completion of screening (66% vs. 92%, respectively), which were sufficiently addressed by extending recruitment to achieve the predetermined statistical power. Thus, it is unlikely that adherence to the protocol substantially affected the outcomes.

Although the 1-step 75-g OGTT test would seem to simplify the diagnostic dilemma, ScreenR2GDM showed that it doubled the number of women who received GDM diagnoses without improving maternal or fetal morbidity compared with the 2-step approach. This introduces considerable burden and costs to patients, clinicians, and medical systems. Glucose monitoring 4 times daily is required to assess treatment response, and women with pharmacologically treated and poorly controlled GDM should have enhanced fetal surveillance with frequent nonstress testing and ultrasonographic biophysical testing beginning at 32 weeks or earlier. The economic savings from 1-step assessment will be surpassed by the considerable costs of additional monitoring associated with doubling the number of women diagnosed with GDM.

Simple is not always better. A noninvasive, reproducible biomarker to detect GDM in pregnant women at increased risk for adverse perinatal outcomes would be ideal. In the interim, an emphasis on prevention and use of the most effective therapies (e.g., insulin rather than metformin or glyburide) is more likely to improve maternal and fetal outcomes and mitigate metabolic consequences in the next generation.