(428) A Comparison of Hemoglobin A1c and the 1-Hour Glucose Challenge Testing in Early Pregnancy

To determine if the Hemoglobin A1c (HgbA1c) and the 50g glucose challenge test (1h GCT) prior to 22 weeks gestation are comparable screening tests for gestational diabetes.

Study Design:

Between 2017-2019, patients with risk factors for hyperglycemia but lacking the diagnosis of pre-gestational diabetes received a 1h GCT and a HgbA1c before 22 weeks (N=136). Patients served as their own controls when comparing HgbA1c vs. 1h GCT (screening tests) and the results of 3h glucose tolerance test (GTT) (confirmatory test). A receiver operating characteristic curve (ROC) was constructed to determine optimal HbA1c cut-offs for screening at less than 22 weeks to guide management of gestational diabetes in early pregnancy. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and likelihood ratios (LR) for gestational diabetes were calculated for a cut-off of HgbA1c > 6.5.  Similar analyses were performed using a cut-off of HgbA1c > 5.8.

 

Results:

The HgbA1c cut-off point as a screening test is compared to the 1 h GCT at < 22 weeks in the table below. 

With the addition of each patient’s respective 3 h GTT results, the sensitivity of HgbA1c cut-off of > 5.8 was 87.50% and specificity was 85.16%. PPV of 26.92% and a NPV of 99.0% were noted. Positive and negative LR were 5.9 (CI 3.6-9.63) and 0.15 (CI 0.02-0.92). 

 

Conclusion:

At a lower threshold than non-pregnant diagnostic cut-offs, the HgbA1c has comparable sensitivity and specificity to the 1h GCT as a screen for gestational diabetes in early pregnancy. It could be considered an alternative to 1h GCT, particularly for patients who cannot tolerate glucose drinks first trimester.  Though a confirmatory test would still need to be performed, a HgbA1c instead of a 1 h GCT prior to 22 weeks may be efficacious particularly in patients with risk factors for hyperglycemia, who need management expeditiously.