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

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  2. Professor Rudy Bilous
Author(s)Law GR, Gilthorpe MS, Secher AL, Temple R, Bilous R, Mathiesen ER, Murphy HR, Scott ER
Publication type Article
ISSN (print)0012-186X
ISSN (electronic)1432-0428
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AbstractAims/hypothesis This study aimed to examine the relationshipbetween average glucose levels, assessed by continuousglucose monitoring (CGM), and HbA1c levels in pregnantwomen with diabetes to determine whether calculationsof standard estimated average glucose (eAG) levelsfrom HbA1c measurements are applicable to pregnantwomen with diabetes.Methods CGM data from 117 pregnant women (89 womenwith type 1 diabetes; 28 women with type 2 diabetes)were analysed. Average glucose levels were calculatedfrom 5–7 day CGM profiles (mean 1275 glucose valuesper profile) and paired with a corresponding (±1 week)HbA1c measure. In total, 688 average glucose–HbA1c pairswere obtained across pregnancy (mean six pairs per participant).Average glucose level was used as the dependentvariable in a regression model. Covariates were gestationalweek, study centre and HbA1c.Results There was a strong association between HbA1c andaverage glucose values in pregnancy (coefficient 0.67 [95%CI 0.57, 0.78]), i.e. a 1% (11 mmol/mol) difference in HbA1ccorresponded to a 0.67 mmol/l difference in average glucose.The random effects model that included gestational week as acurvilinear (quadratic) covariate fitted best, allowing calculationof a pregnancy-specific eAG (PeAG). This showed that anHbA1c of 8.0% (64mmol/mol) gave a PeAG of 7.4–7.7mmol/l(depending on gestational week), compared with a standardeAG of 10.2 mmol/l. The PeAG associated with maintainingan HbA1c level of 6.0% (42 mmol/mol) during pregnancy wasbetween 6.4 and 6.7 mmol/l, depending on gestational week.Conclusions/interpretation The HbA1c–average glucose relationshipis altered by pregnancy. Routinely generatedstandard eAG values do not account for this differencebetween pregnant and non-pregnant individuals and, thus,should not be used during pregnancy. Instead, the PeAGvalues deduced in the current study are recommended forantenatal clinical care.Keywords Average glucose
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