1. A cut-off value of ≥ 135 mg/dL for the glucose challenge test demonstrated a superior combination of sensitivity, specificity, positive predictive value and positive likelihood ratio compared to cut-offs of ≥130 or 140 mg/dL.
2. Cut-offs of ≥130, 135 and 140 mg/dL were highly sensitive for gestational diabetes mellitus in twin pregnancies.
Evidence Rating Level: 2 (Good)
Study Rundown: Gestational diabetes mellitus (GDM) is a relatively common condition in pregnancy. This is thought to be related to diabetogenic pregnancy-related hormonal changes that ensure adequate nutrients for the growing fetus. GDM has been shown to be associated with such complications as preeclampsia, macrosomia, operative delivery, and neonatal mortality. Current ACOG guidelines recommend screening low or normal-risk women at 24-28 weeks gestation with a glucose challenge test (GCT), a 50 gram oral glucose load, and measuring plasma glucose at 1 hour. A positive screen, defined as ≥ 130, 135, or 140 mg/dL depending on the organization, is followed by a 3-hour oral glucose tolerance test (GTT), which is diagnostic for GDM. Some organizations recommend a one-step approach with a 2 hour oral GTT instead. Prior work has shown that twin pregnancies were more likely to have false-positive GCTs, suggesting that different guidelines may be appropriate for this population. The present study is the first to attempt to identify the appropriate cut-off for twin pregnancies and found that a cut-off of ≥135 mg/dL was best able to identify all cases while minimizing false positives.
Limitations of the study include retrospective design, small number of patients with GDM and a patient population disproportionately comprised of IVF or ART pregnancies, which limits power and generalizability. Larger, prospective investigation to identify appropriate cut-off values for twin and other multiple gestation pregnancies is merited.
In-Depth [retrospective cohort study]: This study evaluated the ability of different cut-off values (≥130, 135, or 140 mg/dL) to accurately identify GDM among 475 women with twin pregnancies undergoing a GCT between 24 and 28 weeks gestation. The primary outcomes of interest were positive GCT results and diagnosis of GDM using a three-hour oral GTT.
Overall, 6.5% of patients were diagnosed with GDM. Both cut-offs of ≥130 and 135 mg/dL identified all cases, but the ≥135 mg/dL cut-off had higher sensitivities of 76.4%, positive predictive value of 22.8%, and positive likelihood of 4.2, all superior to those of the ≥130 mg/dL cut-off.
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