Translating HbA1c measurements into estimated average glucose values in pregnant women with diabetes

Law, Graham R. and Gilthorpe, Mark S. and Secher, Anna L. and Temple, Rosemary and Bilous, Rudolf and Mathiesen, Elisabeth R. and Murphy, Helen R. and Scott, Eleanor M. (2017) Translating HbA1c measurements into estimated average glucose values in pregnant women with diabetes. Diabetologia, 60 (4). pp. 618-624. ISSN 0012-186X

Full content URL: http://doi.org/10.1007/s00125-017-4205-7

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Abstract

Aims/hypothesis

This study aimed to examine the relationship between average glucose levels, assessed by continuous glucose monitoring (CGM), and HbA1c levels in pregnant women with diabetes to determine whether calculations of standard estimated average glucose (eAG) levels from HbA1c measurements are applicable to pregnant women with diabetes.

Methods

CGM data from 117 pregnant women (89 women with type 1 diabetes; 28 women with type 2 diabetes) were analysed. Average glucose levels were calculated from 5–7 day CGM profiles (mean 1275 glucose values per profile) and paired with a corresponding (±1 week) HbA1c measure. In total, 688 average glucose–HbA1c pairs were obtained across pregnancy (mean six pairs per participant). Average glucose level was used as the dependent variable in a regression model. Covariates were gestational week, study centre and HbA1c.

Results

There was a strong association between HbA1c and average glucose values in pregnancy (coefficient 0.67 [95% CI 0.57, 0.78]), i.e. a 1% (11 mmol/mol) difference in HbA1c corresponded to a 0.67 mmol/l difference in average glucose. The random effects model that included gestational week as a curvilinear (quadratic) covariate fitted best, allowing calculation of a pregnancy-specific eAG (PeAG). This showed that an HbA1c of 8.0% (64 mmol/mol) gave a PeAG of 7.4–7.7 mmol/l (depending on gestational week), compared with a standard eAG of 10.2 mmol/l. The PeAG associated with maintaining an HbA1c level of 6.0% (42 mmol/mol) during pregnancy was between 6.4 and 6.7 mmol/l, depending on gestational week.

Conclusions/interpretation

The HbA1c–average glucose relationship is altered by pregnancy. Routinely generated standard eAG values do not account for this difference between pregnant and non-pregnant individuals and, thus, should not be used during pregnancy. Instead, the PeAG values deduced in the current study are recommended for antenatal clinical care.

Keywords:Average glucose, Continuous glucose monitoring, Estimated average glucose, Gestation, HbA1c, Pregnant, Type 1 diabetes, Type 2 diabetes
Subjects:G Mathematical and Computer Sciences > G311 Medical Statistics
Divisions:College of Social Science > School of Health & Social Care
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ID Code:29516
Deposited On:11 Nov 2017 17:33

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