Abstract
Aims/hypothesisThis 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.MethodsCGM 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.ResultsThere 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/interpretationThe 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.
Highlights
MethodsThe relationship between HbA1c and average glucose levels has been explored in many studies, most making use of intermittent capillary blood glucose measurements [1,2,3,4,5,6]
If we were to use the A1CDerived Average Glucose (ADAG) formula, an HbA1c of 6.0% (42 mmol/mol) would equate to an estimated average glucose (eAG) of 7 mmol/l irrespective of the gestational week, whereas it would equate to a lower pregnancy-specific eAG (PeAG) using our pregnancy-specific equation
This difference is more pronounced at higher levels of HbA1c, where an HbA1c of 8.0% (64 mmol/mol) equates to a PeAG of 7.7 mmol/l
Summary
MethodsThe relationship between HbA1c and average glucose levels has been explored in many studies, most making use of intermittent capillary blood glucose measurements [1,2,3,4,5,6]. HbA1c is considered unreliable for assessing glucose control during pregnancy owing to physiological changes that may be attributed to increased red cell production, shortened red cell life span, reduced red cell affinity for glucose, iron deficiency and iron supplementation [13,14,15,16,17]. This has led to uncertainty over the role of HbA1c for blood glucose assessment in pregnancy [18], with key bodies [19, 20] advising that it should not be used for diagnosing diabetes in pregnancy, and the National Institute for Health and Care Excellence (NICE) in the UK recommending that it should not be routinely used to assess glucose control in pregnancy in women with established diabetes [20]. Anecdotal reports suggest that clinicians and patients are using the standard eAG value, which is reported with HbA1c levels, during pregnancy, despite it being derived from data from non-pregnant adults
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