Gestational Diabetes Screening, who’s “Best Evidence”

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The National Institutes of Health consensus panel has determined that the one-step screening test for gestational diabetes results in greater numbers of positive outcomes than the traditional two-step method. The one-step requires a 3-hour glucose tolerance test. The traditional method specifies screening with a non-fasting glucose challenge testing at one hour. Only the positives then go on to the 3-hour GTT. The one-step approach results in 15% to 20% positives, whereas the traditional two-step protocol results in only 5% to 6% positives.[1] The panel concluded that the current data do not indicate whether the one-step protocol improves outcome or diagnostic accuracy.

From the data, one might wonder if the non-fasting screen misses significant numbers resulting in fewer diagnoses of gestational diabetes – a matter of sensitivity. Alternatively, the 3-hour test may lack specificity resulting in false positives. Looking further in the literature,[2] O’Shea and O’Connor in Ireland argue in favor of an HbA1c in the second trimester.    The American College of Obstetrics and Gynecology recommends screening by history, risk factors or the non-fasting 50g glucose challenge.[3] The US Preventive Services Task Force argues that there is insufficient evidence for or against anti-natal screening for diabetes. Mayo Clinic states that history and risk factor screening may be sufficient for women under 25.[4]

Obviously, the increasing obesity among young women poses a threat. Hospitals have broadly adopted the one-step approach. One wonders if the hospitals favor the more expensive option with higher numbers of positive results for business reasons. You might conversely ask if the US Preventive Services Task Force leans in the opposite direction for reasons of cost containment.

There is nonetheless a consensus that the definitive test for gestational diabetes is the 3-hour GTT with proven correlation to outcome. Is this not an argument in favor of professional judgment in selecting when to do the GTT rather than elusive best evidence? --- Who's best evidence and who’s viewpoint?

 

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[1] http://tinyurl/c642s5e

[2] www.ncbi.nlm.nih.gov/pubmed/22838107

[3]http://www.acog.org/Resources%20And%20Publications/Committee%20Opinions/Committee%20on%20Obstetric%20Practice/Screening%20and%20Diagnosis%20of%20Gestational%20Diabetes%20Mellitus.aspx

[4] http://www.mayoclinic.com/health/gestational-diabetes/DS00316/DSECTION=tests-and-diagnosis