Antenatal haemoglobin A1c centiles: does one size fit all?

Area of Science:

• Obstetrics and Gynaecology
• Endocrinology
• Public Health

Background:

• Haemoglobin A1c (HbA1c) screening is standard in New Zealand for detecting pre-existing hyperglycaemia before 20 weeks gestation.
• A normal HbA1c is defined as <5.9% (41 mmol/mol), based on non-pregnant population ranges.

Purpose of the Study:

• To establish pregnancy-specific HbA1c centiles stratified by gestational age and maternal ethnicity.
• To inform more accurate screening for hyperglycaemia during pregnancy.

Main Methods:

• A population-based observational study utilizing data from 6800 pregnancies in New Zealand (2008-2010).
• HbA1c centiles were calculated from electronic laboratory and clinical records for pregnancies without pre-existing or gestational diabetes.
• Longitudinal data from 112 women were used to verify trends.

Main Results:

• HbA1c levels demonstrated a decline with increasing gestation, reaching a nadir at 24 weeks.
• The 97.5th centile for HbA1c in European women varied by gestation (e.g., 5.76% at 8 weeks, 5.65% at 24 weeks).
• Non-European women (Māori, Pacific, Asian) exhibited higher mean HbA1c levels compared to European women, with statistically significant differences.

Conclusions:

• The current New Zealand HbA1c threshold of ≥5.9% (41 mmol/mol) for identifying hyperglycaemia exceeds the 97.5th centile for European and 'Other' ethnic groups.
• Utilizing population-specific HbA1c centiles adjusted for gestation and ethnicity could improve the management of hyperglycaemia in pregnancy.