Is fasting plasma glucose in early pregnancy a better predictor of adverse obstetric outcomes than glycated haemoglobin?

Objectives: To determine, in a multi-ethnic cohort, the suitability of first-trimester fasting plasma glucose and HbA1c levels in non-diabetic range to identify women without diabetes at increased pregnancy risk.

Study Design: A retrospective analysis of a prospective cohort between April 2013 and September 2015. Universal testing for fasting plasma glucose and HbA1c levels at the first antenatal blood sampling was performed and women were screened for gestational diabetes mellitus at 24-28 weeks' gestation. Primary outcomes were macrosomia and pre-eclampsia, and secondary outcomes preterm delivery, Caesarean section and large-for-gestational age. Different fasting plasma glucose and HbA1c cut-off levels were assessed for associations with outcomes.

Results: 1,228 pregnancies were included for outcome analysis. After adjustment for potential confounders, no association was found between fasting plasma glucose levels and pregnancy outcomes. Women with an HbA1c ≥5.8% (39.9 mmol/mol) showed an increased risk of macrosomia (OR 2.69, 95% CI 1.16-6.24); an HbA1c ≥5.9% (41 mmol/mol) threshold was independently associated with a three-fold risk of pre-eclampsia (95% CI 1.03-9.9) and an HbA1c ≥6.0% (42.1 mmol/mol) with a four-fold risk of large-for-gestational age (95% CI 1.49-11.07).

Conclusions: In a multi-ethnic population, first-trimester fasting plasma glucose levels were not a better predictor of pregnancy complications than HbA1c. Further, an early HbA1c ≥5.8% (39.9 mmol/mol) threshold is already associated with an increased risk of macrosomia.