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Optimal A1c for Detecting Diabetes in Early Pregnancy

Sep 19, 2014
 

An HbA1c higher than 5.9% was a more accurate indicator for diabetes in pregnant patients…. 

Since pregnant women are at high risk of diabetes, early intervention may be beneficial in this patient population. Currently, an HbA1c ≥6.5% (48 mmol/mol) is recommended to define diabetes in pregnancy, but this figure was based on non-pregnancy data.

Using an early oral glucose tolerance test (OGTT) before 20 weeks’ gestation, a study was conducted to determine the optimal HbA1c threshold for detecting diabetes early on in pregnant women. Researchers also observed the relationship of pregnancy outcomes to this threshold.

During 2008-2010, a total of 16,122 pregnant women in Christchurch, New Zealand were offered an HbA1c measurement with their first antenatal bloods at a median 47 days’ gestation. The researchers also collected pregnancy outcome data, and a subset of patients completed an early OGTT. Using World Health Organization criteria, they assessed HbA1c performance in these patients.

An early OGTT was performed on 974 (23%) patients out of 4,201 patients. There were 15 cases of diabetes in this subset, and the HbA1c was ≥5.9% (41 mmol/mol) in all cases and <6.5% (<48 mmol/mol) in 7 cases. Also, this HbA1c threshold was 98.4% (95% CI 97–99.9%) specific for gestational diabetes mellitus (GDM) with a positive predictive value of 52.9% at <20 weeks’ gestation. In the total cohort, which excluded the women that were referred for GDM management, there were 200 women with an HbA1c of 5.9–6.4% (41–46 mmol/mol) and 8,174 women with an HbA1c <5.9% (<41 mmol/mol). Out of these two groups, the women in the former group experienced poorer pregnancy outcomes with a relative risk (95% CI) of 2.67 (1.28–5.53) for major congenital anomaly, 2.42 (1.34–4.38) for preeclampsia, 2.47 (1.05–5.85) for shoulder dystocia, and 3.96 (1.54–10.16) for perinatal death.

HbA1c measurements were performed on a large number of participants, but only a small percentage of patients undertook the OGTT. Nonetheless, all pregnant women with diabetes who also had a significantly increased risk of experiencing adverse pregnancy outcomes were identified with an HbA1c ≥5.9% (≥41 mmol/mol), making this value the optimal HbA1c threshold for detecting diabetes in early pregnancy.

Practice Pearls:
  • All pregnant women who developed diabetes had an HbA1c ≥5.9%.
  • Pregnant women with an HbA1c of 5.9–6.4% experienced poorer pregnancy outcomes than those with an HbA1c <5.9%.
  • This study indicated that an HbA1c ≥5.9% was the optimal HbA1c threshold for detecting diabetes in early pregnancy.

Published online on Sep 4, 2014 in Diabetes Care.