Screening approach for gestational diabetes in twin pregnancies

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).

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.

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.

In twin pregnancies, the optimal 1-hour, 50-g GCT screening cutoff appears to be ≥135 mg/dL.