Current practice is to screen all pregnant patients for gestational diabetes (GDM, a condition that affects about 10% of pregnancies), regardless of prior history. However, among patients with a normal 1-hour 50-gram glucose screen (GCT) in a prior pregnancy, the risk of being diagnosed with GDM in a subsequent pregnancy is less than 4%. The tool below allows providers to target screening to the highest risk patients among those with no history of diabetes and a normal 1h-GCT (<140 mg/dL) in a preceding pregnancy. Using a risk cutoff of 15%, the tool has a negative predictive value (NPV) of 97% and a positive predictive value (PPV) of 29% for GDM in a subsequent pregnancy.
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At 15% threshold in our model, NPV is 97% and PPV is 29%. This means that 97% of those categorized as "low risk" (i.e. calculated risk of GDM less than 15%) did not go on to develop GDM in a subsequent pregnancy. Among patients at or above the 15% risk threshold, 29% developed GDM in a subsequent pregnancy.