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Clinical Chemistry and Laboratory Medicine (CCLM)

Published in Association with the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM)

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Trimester-specific reference intervals for haemoglobin A1c (HbA1c) in pregnancy

Catherine O’Connor1 / 2 / Lisa Ann Owens1 / Louise Carmody1 / Gloria Avalos1 / Laura Nestor1 / Katherine Lydon1 / Fidelma Dunne1

1Department of Medicine, College of Medicine Nursing and Health Sciences, National University of Ireland, Galway, Ireland

2Department of Clinical Biochemistry, Galway University Hospitals, Newcastle Road, Galway, Ireland

Corresponding author: Paula Mary O’Shea, Department of Clinical Biochemistry, Galway University Hospitals, Newcastle Road, Galway, Ireland Phone: +353 91 544607

Citation Information: Clinical Chemistry and Laboratory Medicine. Volume 50, Issue 5, Pages 905–909, ISSN (Online) 1437-4331, ISSN (Print) 1434-6621, DOI: https://doi.org/10.1515/cclm.2011.397, November 2011

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Background: Diabetes in pregnancy imposes additional risks to both mother and infant. These increased risks are considered to be primarily related to glycaemic control which is monitored by means of glycated haemoglobin (HbA1c). The correlation of HbA1c with clinical outcomes emphasises the need to measure HbA1c accurately, precisely and for correct interpretation, comparison to appropriately defined reference intervals. Since July 2010, the HbA1c assay in Irish laboratories is fully metrologically traceable to the IFCC standard. The objective was to establish trimester-specific reference intervals in pregnancy for IFCC standardised HbA1c in non-diabetic Caucasian women.

Methods: The authors recruited 311 non-diabetic Caucasian pregnant (n=246) and non-pregnant women (n=65). A selective screening based on risk factors for gestational diabetes was employed. All subjects had a random plasma glucose <7.7 mmol/L and normal haemoglobin level. Pregnancy trimester was defined as trimester 1 (T1, n=40) up to 12 weeks +6 days, trimester 2 (T2, n=106) 13–27 weeks +6 days, trimester 3 (T3, n=100) >28 weeks to term.

Results: The normal HbA1c reference interval for Caucasian non-pregnant women was 29–37 mmol/mol (Diabetes Control and Complications Trial; DCCT: 4.8%–5.5%), T1: 24–36 mmol/mol (DCCT: 4.3%–5.4%), T2: 25–35 mmol/mol (DCCT: 4.4%–5.4%) and T3: 28–39 mmol/mol (DCCT: 4.7%–5.7%). HbA1c was significantly decreased in trimesters 1 and 2 compared to non-pregnant women.

Conclusions: HbA1c trimester-specific reference intervals are required to better inform the management of pregnancies complicated by diabetes.

Keywords: glycated haemoglobin (HbA1c); pregnancy; reference intervals; trimester

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