title: Translating HbA1cmeasurements into estimated average glucose values in pregnant women with diabetes.
abstract: This study aimed to examine the relationship between average glucose levels, assessed by continuous glucose monitoring (CGM), and HbA1clevels in pregnant women with diabetes to determine whether calculations of standard estimated average glucose (eAG) levels from HbA1cmeasurements are applicable to pregnant women with diabetes.
  
  
  
  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) HbA1cmeasure. In total, 688 average glucose-HbA1cpairs 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.
  
  
  
  There was a strong association between HbA1cand average 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 a curvilinear (quadratic) covariate fitted best, allowing calculation of a pregnancy-specific eAG (PeAG). This showed that an HbA1cof 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 HbA1clevel of 6.0% (42 mmol/mol) during pregnancy was between 6.4 and 6.7 mmol/l, depending on gestational week.
  
  
  
  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.
authors.affiliation: School of Health and Social Care, University of Lincoln, Lincoln, UK.
authors.forename: Graham R
authors.initials: GR
authors.lastname: Law
authors.affiliation: Division of Epidemiology and Biostatistics, Leeds Institute of Cardiovascular and Metabolic Medicine, Clarendon Way, University of Leeds, Leeds, LS2 9JT, UK.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Gilthorpe
authors.affiliation: Institute for Clinical Medicine, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Anna L
authors.initials: AL
authors.lastname: Secher
authors.affiliation: Elsie Bertram Diabetes Centre, Norfolk and Norwich University Hospital NHS Trust, Norwich, UK.
authors.forename: Rosemary
authors.initials: R
authors.lastname: Temple
authors.affiliation: Newcastle University Medicine Malaysia, Johor, Malaysia.
authors.forename: Rudolf
authors.initials: R
authors.lastname: Bilous
authors.affiliation: Institute for Clinical Medicine, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Elisabeth R
authors.initials: ER
authors.lastname: Mathiesen
authors.affiliation: Norwich Medical School, University of East Anglia, Norwich, UK.
authors.forename: Helen R
authors.initials: HR
authors.lastname: Murphy
authors.affiliation: Division of Epidemiology and Biostatistics, Leeds Institute of Cardiovascular and Metabolic Medicine, Clarendon Way, University of Leeds, Leeds, LS2 9JT, UK. e.m.scott@leeds.ac.uk.
authors.forename: Eleanor M
authors.initials: EM
authors.lastname: Scott
mesh_terms: D000293:Adolescent; D000328:Adult; D001786:Blood Glucose / Q000378:metabolism*; D015190:Blood Glucose Self-Monitoring; D003922:Diabetes Mellitus, Type 1 / Q000097:blood* / Q000378:metabolism*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood* / Q000378:metabolism*; D005260:Female; D006442:Glycated Hemoglobin / Q000378:metabolism*; D006801:Humans; D008875:Middle Aged; D018743:Perinatal Care; D011247:Pregnancy; D055815:Young Adult
chemical_list: D001786:Blood Glucose; D006442:Glycated Hemoglobin
keywords: Average glucose; Continuous glucose monitoring; Estimated average glucose; Gestation; HbA1c; Pregnant; Type 1 diabetes; Type 2 diabetes