Evidence for the utility of antenatal HbA1c to predict early postpartum diabetes after gestational diabetes in South Africa

Aim To evaluate antenatal HbA1c at diagnosis and in the 4 weeks preceding delivery to predict early postpartum diabetes mellitus (DM) in women with Gestational Diabetes Mellitus (GDM). Methods Seventy-eight women with GDM were prospectively assessed. The ability of HbA1c at GDM diagnosis (t1) and in the 4 weeks preceding delivery (t2) to predict DM 6-12 weeks after delivery was investigated. Glucose assessment was performed between November 1, 2015, and November 1, 2016 at Tygerberg Hospital (TH), Cape Town, South Africa (SA). Individuals with known pre-existing diabetes were excluded. Results HbA1c of 6.2% (44 mmol/mol) and 6.5% (48 mmol/mol) at t1 predicted DM with sensitivities of 95% and 90% and specificities of 62% and 70% respectively. At t2 the best cut-off for HbA1c, in accordance with t1, was also 6.2% (44 mmol/mol; sensitivity 92%, specificity 56%). Nineteen of the 29 women with suspected pre-gestational DM had HbA1c levels ≥ 6.5% (48 mmol/mol) at t1. The increased risk for postpartum DM with HbA1c ≥ 6.2% (44 mmol/mol) was four-fold (OR 3.97 CI 2.08-7.59p < 0.001) at t1 and five-fold (OR 5.08 CI 1.60-16.25 p = 0.006) at t2. Conclusion HbA1c lower than 6.5% (48 mmol/mol) predicts postpartum DM in women with GDM. HbA1c can serve as instrument to improve postpartum follow-up.