Screening approach for gestational diabetes in twin pregnancies

OBJECTIVE: The objective of this study was to evaluate the ideal cutoff for the glucose challenge test (GCT) in twin pregnancies undergoing screening for gestational diabetes mellitus (GDM). STUDY DESIGN: A historical cohort of patients with twin pregnancies were identified from 1 maternal-fetal medicine practice from 2005 through 2013. All patients were administered a 1-hour, 50-g GCT between 24-28 weeks' gestation. All patients with a GCT of ≥130 mg/dL underwent a 3-hour, 100-g oral glucose tolerance test. The diagnosis of GDM was made if 2 of the 4 values on the oral glucose tolerance test were abnormal (Carpenter and Coustan). The testing characteristics of the GCT for diagnosis of GDM were evaluated using 3 selected cutoffs: ≥130, ≥135, and ≥140 mg/dL. We excluded all patients diagnosed with GDM <24 weeks. RESULTS: In all, 475 patients with twin pregnancies underwent a GCT between 24-28 weeks. The incidence of GDM was 6.5%. The positive screen rate using the 3 selected cutoffs were: ≥130 mg/dL, 34.7%; ≥135 mg/dL, 28.6%; and ≥140 mg/dL, 23.4%. A GCT cutoff of ≥135 mg/dL maintained 100% sensitivity, with a specificity of 76.4%. Using this cutoff, the positive predictive value was 22.8% and the negative predictive value was 100%. Compared to a cutoff of ≥130 mg/dL, a cutoff of ≥135 mg/dL resulted in 6.1% less patients testing positive while maintaining the same 100% sensitivity. CONCLUSION: In twin pregnancies, the optimal 1-hour, 50-g GCT screening cutoff appears to be ≥135 mg/dL.