Aims: Despite current treatment strategies, gestational diabetes mellitus (GDM) remains a major risk factor for pregnancy complications. We examined whether the HbA1c measured at the time of oral glucose tolerance test (OGTT) predicts residual risk of adverse outcomes in women with treated GDM.

Methods: Women with GDM (defined using the New Zealand criteria) enrolled in the Diabetes in Pregnancy Registry in South Auckland, New Zealand at ≥ 20 weeks gestation were included. Glycaemic targets used were fasting ≤5.0 mmol/l and 2-hour post-meal ≤6.7 mmol/l.

Results: Of the 1403 women enrolled, 304 (21.7%) had an HbA1c 41-49 mmol/mol (5.9-6.6%). Women with higher HbA1c were significantly older, with higher BMI and fasting and 2-hour OGTT values. They were more likely to be multiparous, of Pacific ethnicity, and have a family history of diabetes. After adjusting for known risk factors, higher HbA1c was associated with increased risk of large for gestational age (LGA) babies (odds ratio (OR) 2.08 (1.47-2.93)) and preeclampsia (OR 2.09 (1.34-3.29)). The OGTT fasting glucose was predictive of LGA (OR 1.61 (1.17-2.21)), but not the 2-hour value (OR 1.12 (0.98-1.28)). The areas under the receiver operating characteristic curves for predicting LGA and preeclampsia by HbA1c, OGTT fasting, OGTT 2-hour, and 1-hour 50g polycose test were: LGA, 0.58 (0.51-0.65), 0.66 (0.59-0.73), 0.45 (0.37-0.52), and 0.59 (0.51-0.66) respectively; preeclampsia, 0.66 (0.57-0.75), 0.58(0.48-0.67), 0.46 (0.35-0.56), and 0.52 (0.42-0.62) respectively.

Conclusions: HbA1c, fasting, and 1-hour glucose at GDM diagnosis predict residual adverse outcomes in treated women with late GDM. Studies are needed to test whether earlier treatment, or targeting the 1-hour post-prandial glucose can reduce this residual risk.


D. Simmons: None. J. Immanuel: None. C. Eagleton: None. J. Baker: None.

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