The use of HbA1c in predicting excessive fetal growth in women at risk of gestational diabetes

  • Robert D'Arcy

Student thesis: Doctoral ThesisDoctor of Philosophy


Introduction Gestational diabetes mellitus (GDM) is associated with excessive fetal growth in later gestation. Traditionally, GDM is diagnosed between 26-28 weeks’ gestation. Subsequent intervention aims to reduce the risk of excessive fetal growth and its associated sequelae. Recent data suggest accelerated fetal growth may begin before 28 weeks’ gestation. We assessed the use of early pregnancy HbA1c in predicting such excessive fetal growth. Secondly, we assessed the performance of ultrasound- measured maternal visceral adipose tissue depth (VAD) in GDM prediction.MethodsHbA1c was measured at <14 weeks gestation in 946 women at risk of GDM as defined by NICE risk factors. Fetal ultrasound was performed at 28 weeks’ gestation alongside a 75g OGTT. GDM was defined using IADPSG/WHO criteria. VAD using ultrasonography was measured at <14 weeks gestation in 122 of these women.Results186 women screened positive for GDM. At diagnosis, GDM pregnancies already demonstrated higher mean adjusted fetal weight percentile than non-GDM pregnancies: (50.9 vs 46.2 p=0.02). This was driven by relative increases in the fetal abdominal circumference percentile in GDM compared with non-GDM pregnancies (mean 54.7 vs 46.2 p=<0.01).Early pregnancy HbA1c was higher in the GDM vs non-GDM group: 35.8 vs 32.9 p=<0.01. A threshold for predicting excessive fetal growth was not identified. Women with GDM had a higher VAD than those without GDM (4.22 vs 3.12 p<0.01). Using ROC analysis, a VAD of 3.98cm achieved a sensitivity of 73.1% and specificity of 72.2% for the later diagnosis of GDM. Women exceeding this threshold were at seven-fold greater odds of GDM. Conclusions These results demonstrate that accelerated fetal growth is evident prior to the diagnosis of GDM. First trimester HbA1c was not useful in identifying these pregnancies. 

Thesis embargoed until 31 December 2023.
Date of AwardDec 2021
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsNorthern Ireland Public Health Agency
SupervisorUna Graham (Supervisor), David McCance (Supervisor) & Michelle McKinley (Supervisor)


  • Gestational diabetes
  • fetal growth
  • HbA1c

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