David B, et al. – The usefulness and efficacy of first–trimester HbA1c were examined in the diagnosis of gestational diabetes (GDM). Investigations suggested that a first–trimester HbA1c did not exhibit sufficient sensitivity or specificity to diagnose GDM. However, the use of a higher and lower threshold could simplify the diagnostic process by reducing the number of oral glucose tolerance test, associated costs, and patient inconvenience.

Methods

• This observational study consisted of pregnant women.
•  All women had a first–trimester HbA1c determination and GDM screening at 24–28 weeks of pregnancy using a two–step approach.
• A ROC curve was drawn to determine the sensitivity and specificity of HbA1c in detecting GDM.
• Moreover, a rule–in rule–out diagnostic algorithm was also proposed.
• The cost of the proposed algorithm was measured.

Results

• Out of 1,195 women, 152 (13.1%) were diagnosed of GDM.
• The area under the ROC curve for HbA1c to detect GDM was 0.679 (95%CI 0.631–0.727). 
•  A rule–out threshold for HbA1c of 4.8% (29 mmol/mol) had 96.7% sensitivity (95%CI 93.9–99.5), 10.1% specificity (95%CI 8.3–12.0) and a negative predictive value of 95.3% (95%CI 91.3–99.3).
•  A rule–in value of 5.6% (38 mmol/mol) had a positive predictive value of 31.6% (95%CI 24.4–38.9), 89.3% specificity (95%CI 87.4–91.2) and 32.9% sensitivity (Reviewer 2, comment 12) (95%CI 25.4–40.4).
•  The low positive predictive value of the rule–in threshold precludes its use for GDM diagnosis, but could be used to identify women at high risk of GDM in whom the diagnosis can be established using a one–step approach. 
• The overall saving of the proposed algorithm would be 6.5% of the total cost with the standard strategy.