First‐trimester glycaemic markers as predictors of gestational diabetes and its associated adverse outcomes: a prospective cohort study

Objective
Gestational diabetes mellitus (GDM) is associated with excessive fetal growth in later gestation. Recent data suggest accelerated growth may begin before 28 weeks' gestation when GDM is typically diagnosed. The identification of pregnancies at risk of early fetal growth would enable early intervention. We assessed the use of early pregnancy HbA1c in predicting excessive fetal growth.

Research Design and Methods
Women were recruited at antenatal booking from a major maternity unit in the UK. HbA1c was measured at <14 weeks gestation in 1243 women at risk of GDM as defined by UK NICE risk factors of whom 1115 underwent OGTT. Women with previous GDM were excluded. Comprehensive fetal ultrasound was performed at 28 weeks' gestation alongside 75 g OGTT in 976 of these women. GDM was defined using WHO criteria. Pregnancy outcomes were extracted from the regional maternity care database.

Results
Two hundred and thirty-six women screened positive for GDM. At diagnosis, GDM pregnancies demonstrated higher adjusted fetal weight percentile than non-GDM pregnancies: (51.8 vs. 46.3, p = 0.008). This was driven by increases in the fetal abdominal circumference percentile in GDM compared with non-GDM pregnancies (55.3 vs. 46.2, p = <0.001). Early pregnancy HbA1c was higher in the GDM versus non-GDM group: (35.7 mmol/mol vs. 32.9 mmol/mol p = <0.01). A threshold for predicting excessive fetal growth was not identified in this cohort.

Conclusions
Accelerated fetal growth is evident prior to the diagnosis of GDM. There remains a need for suitable methods of early identification of pregnancies at high risk for early accelerated fetal growth due to GDM. First-trimester HbA1c was not useful in identifying these pregnancies.