Women with an HbA 1c of 41–49 mmol/mol (5.9–6.6%): a higher risk subgroup that may benefit from early pregnancy intervention

Aims To examine whether women with an HbA 1c of 41–49 mmol/mol (5.9–6.6%) at diagnosis of gestational diabetes are higher risk than women with an HbA 1c of < 41 mmol/mol (5.9%) and whether pregnancy outcomes are improved if treated at < 24 weeks' gestation. Methods This was an observational study of women with gestational diabetes diagnosed by early HbA 1c screening or subsequent oral glucose tolerance test at < 34 weeks' gestation who delivered at National Women's Health, Auckland, from July 2012 to June 2014. Data were extracted from the hospital database. Women with HbA 1c 41–49 mmol/mol (5.9–6.6%) were divided into those seen < 24 weeks (Early, n  = 134) and those seen ≥ 24 weeks (Later, n  = 151). Those with HbA 1c  < 41 mmol/mol (5.9%) were labelled Other GDM ( n  = 661). Results The Early and Later groups, compared with Other GDM , had more Polynesian and fewer (non‐Indian) Asian women, higher BMI and more required medication ( P  < 0.001). More were smokers ( P  = 0.007, 0.02) and more had chronic hypertension ( P  < 0.001, 0.02). There were higher rates of adverse outcomes in the Later group than the Other GDM group (pre‐eclampsia 8.0% vs. 2.4%, P  = 0.001, preterm birth 16.6% vs. 8.2%, P  = 0.002, neonatal admission 15.5% vs. 9.2%, P  = 0.02). Outcomes were similar between the Early group and Other GDM group (pre‐eclampsia 1.5% vs. 2.4%, P  = 0.5, preterm birth 10.5% vs. 8.2% P  = 0.4, neonatal admission 13.6% vs. 9.2%, P  = 0.12). Comparing the Early and Later groups, the Early group had less pre‐eclampsia, 1.5% vs. 8.0%, adjusted P  = 0.03. Other outcomes were not statistically different. Conclusions An HbA 1c of 41–49 mmol/mol (5.9–6.7%) identifies a higher‐risk group of women with gestational diabetes. Overall, our data support early treatment of women with an HbA 1c  ≥ 41 mmol/mol (5.9%).