(HealthDay News) — The optimal one-hour 50g glucose challenge test (GCT) screening cut-off for gestational diabetes mellitus (GDM) is ≥135mg/dL in twin pregnancies, according to a study published online October 14 in the American Journal of Obstetrics & Gynecology.

Andrei Rebarber, MD, from the Icahn School of Medicine at Mount Sinai in New York City, and colleagues examined the ideal GCT cut-off in twin pregnancies undergoing GDM screening from a historical cohort of patients. Four hundred seventy-five patients underwent a one-hour 50g GCT at 24–28 weeks of gestation, and those with a GCT of ≥130mg/dL underwent a three-hour 100g oral glucose tolerance test. The testing characteristics of the GCT for GDM diagnosis were assessed at cut-offs of ≥130mg/dL, ≥135mg/dL, and ≥140mg/dL.

The researchers found that the incidence of GDM was 6.5%. The positive screen rates were: ≥130mg/dL, 34.7%; ≥135mg/dL, 28.6%; and ≥140, 23.4%. With a cut-off of ≥135mg/dL, sensitivity and specificity were 100 and 76.4%, respectively. The positive and negative predictive values were 22.8 and 100%, respectively, at this cut-off. A cut-off of ≥135mg/dL vs. ≥130mg/dL resulted in 6.1% fewer patients testing positive, without affecting sensitivity.

“In twin pregnancies, the optimal one-hour 50g GCT screening cut-off appears to be ≥135mg/dL,” the authors write.

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