Predictive Cutoffs of 1-Hour GCT Prior to 16 Weeks in Diagnosing Carbohydrate Intolerance in Early Gestation [36L]

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Early pregnancy screening for undiagnosed type 2 diabetes (DM) is commonly performed using the same criteria used at mid-gestation. However, characteristics of early GCT have not been well described. We compared the predictive values of different cutoffs of early versus late GCT.


Single center retrospective cohort study of women with a positive 1-hour GCT (>130 mg/dL) prior to 16 weeks gestation (eGCT) or between 24 and 28 weeks of gestation (lGCT). eGCT was performed in high-risk patients. All women with a positive GCT received a 3-hour glucose tolerance test (GTT). Carpenter-Coustan criteria were used to diagnose DM. Sensitivity and specificity were calculated for eGCT and lGCT cutoffs from 130 to 195 mg/dL.


Three thousand two hundred seventy-one women met study criteria, of whom 228 received eGCT and 3,043 received lGCT. Overall prevalence of GDM was 18% (23% early diagnosis, 17% late diagnosis). The sensitivity and specificity were (cutoff: sensitivity/specificity; eGCT versus lGCT) 130: 100%/1%, versus 99%/1%; 135: 98%/8%, versus 96%/12%; 140: 92%/21% versus 87%/31%; 150: 73%/49% versus 66%/62%. Sensitivity and specificity of eGCT to predict mid-gestation GDM diagnosis were 130: 100%/0%; 135: 94%/11%; 140: 90%/24%; 150: 68%/52%; 160: 35%/83%; 170: 10%/91%; 180: 3%/97%; 185: 0%/100%.


Similar to the lGCT, eGCT cutoffs of 130–140 mg/dL have high sensitivity with poor specificity. For patients without early diagnosis of DM, an eGCT cutoff >180 is highly predictive of mid-gestation GDM. Given the poor specificity, other screening tests such as 2-hour GTT or standard screening combined with HgBA1C could be studied as alternatives.

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