Universal HbA1c screening and gestational diabetes: a comparison with clinical risk factors

Background: Screening strategies for gestational diabetes mellitus (GDM), particularly early GDM, have traditionally relied upon the use of clinical risk factors (CRFs). Although commonly used in nonpregnant patients, HbA1c screening is not widely used despite reports of abnormal HbA1c values being predictive of GDM development. The aims of this study are to assess the utility of universal HbA1c screening in predicting GDM and to compare universal screening to targeted CRF-based screening for the diagnosis of GDM. Study design: This is a retrospective cohort study of patients undergoing universal HbA1c screening at ≤16 completed weeks gestation with a singleton pregnancy between December 2016 and April 2018 at a single urban tertiary care center. Patients with preexisting diabetes (HbA1c ≥6.5%) or patients who did not have glucose tolerance testing were excluded. Patients with HbA1c 5.7–6.4% underwent early two-step GDM screening. Positive screens were diagnosed with early GDM. Normal early screeners underwent repeat 3rd trimester screening. Clinical risk factors for early GDM screening at our institution prior to universal screening were history of GDM, body mass index (BMI) ≥40 kg/m², prior macrosomia (birth weight ≥4000 g) or stillbirth, and polycystic ovary syndrome. Multivariable regression was performed to assess the relationship between HbA1c and GDM. The predictive ability of universal HbA1c screening compared to that of CRFs was evaluated by testing for differences in the area under the curve (AUC) of receiver operating curves (ROCs). Results: One thousand nine hundred and fifteen patients met inclusion criteria. Two hundred and thirty-one (12.1%) patients had an elevated HbA1c ≥5.7%. Patients with elevated HbA1c were more likely to be older, Black, or obese compared with patients with normal HbA1c values. After adjusting for Black race, BMI, age, and public insurance, the odds of GDM development are 3.50 (95%CI 2.26–5.39) times higher among patients with HbA1c ≥5.7% compared to those with a normal HbA1c. Clinical risk factors for early glucose screening were present in 33% of patients with an elevated HbA1c. The AUC of CRF screening and HbA1c ≥5.7% was 0.72 and 0.75, respectively (p=.07), after controlling for Black race, BMI, maternal age, and insurance. Conclusions: An elevated HbA1c is associated with an increased risk of GDM. Universal HbA1c screening performs as favorably as CRF based screening for the prediction of GDM.