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    Newly proposed GDM screening protocol: unanswered questions remain

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    Charles J. Lockwood, MD, MHCM
    You would think that after 40 years of study and practice, all issues surrounding the management of gestational diabetes mellitus (GDM) would be settled. Based on criteria derived from studies in the early 1970s by O'Sullivan and Mahan, the American College of Obstetricians and Gynecologists (ACOG) estimates that about 2% to 5% of our pregnant population is affected.1 Now a vigorous debate has developed concerning whether to adjust traditional GDM screening methods and criteria.2 At stake is a possible tripling in the number of patients defined as affected by GDM and a substantial increase in the cost of prenatal care.

    Evolution of current practice

    The basis for our current screening strategy derives from the pioneering work of O'Sullivan and Mahan who established thresholds for fasting, 1-hour, 2-hour, and 3-hour glucose values that predicted a 50% risk of future diabetes.3

    Although the original intent of 3-hour glucose tolerance testing (GTT) was to predict future diabetes, the current focus is identification of pregnant women at risk for adverse pregnancy outcomes such as macrosomia, neonatal hyperbilirubinemia, shoulder dystocia, and birth injury.4

    Shockingly, the clinical value of GDM screening and management only recently has been established by randomized trials.5,6 And while we expend ever-greater efforts toward managing glucose values during pregnancy, less effort and success has been realized in achieving universal postpartum screening and long-term prevention, the rationale behind O'Sullivan and Mahan's original work.7

    There has always been debate surrounding the proper methods for screening for GDM. Indeed, it has taken multiple international conferences to derive the screening system we use today: a system of essentially universal screening with a 1-hour, 50-g glucose challenge test followed by a diagnostic 3-hour, 100-g GTT when patients fail the 1-hour screen. Once a woman has been diagnosed with GDM, as a field we have embraced very aggressive glucose monitoring and control while largely ignoring women whose testing is normal or borderline. However, the reality is that glucose tolerance in pregnancy is a continuum and GDM is not a discrete disease. Indeed, one abnormal value on a 3-hour GTT is associated with adverse pregnancy outcomes.8

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    Charles J. Lockwood, MD, MHCM
    Dr. Lockwood, Editor-in-Chief, is Dean of the Morsani College of Medicine and Senior Vice President of USF Health, University of South ...

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