Underestimation of risk for large babies in rural and remote Australia: Time to change plasma glucose collection protocols

Highlights • In remote Australia, many women with GDM are missed due to test sample instability. • FC tubes stabilise glucose but markedly increase GDM diagnosis in lower-risk women. • Adjustment of FC results lowered GDM and improved risk-assessment for a large baby.
Aims Preanalytical glycolysis in oral glucose tolerance tests (OGTT) leads to substantial underestimation of gestational diabetes mellitus (GDM) and hence risk for large-for-gestational-age (LGA) babies. This paper quantified the impact of glycolysis on identification of LGA risk in a prospective rural and remote Australian cohort. Methods For 495 women, OGTT results from room temperature fluoride-oxalate (FLOX) tubes were algorithmically corrected for estimated glycolysis compared to 1) the Hyperglycaemia and Adverse Pregnancy Outcomes (HAPO) study protocol (FLOX tubes in ice-slurry); and 2) room temperature fluoride-citrate (FC) tubes. GDM was defined by International Association of the Diabetes and Pregnancy Study Groups (IADPSG) criteria. Unadjusted and corrected OGTT were related to LGA outcome. Results Correction for FC tubes increased GDM incidence from 9.7% to 44.6%. After correction for HAPO protocol, GDM incidence was 27.7% and prediction of LGA risk (RR 1.82, [1.11–2.99]) improved compared to unadjusted rates (RR 1.12, [0.51–2.47]). To provide similar results for FC tube correction (29.3% GDM; RR 1.81, [1.11–2.96]) required + 0.2 mmol/L adjustment of IADPSG criteria. Conclusions FC tubes present a practical alternative to the HAPO protocol in remote settings but give + 0.2 mmol/L higher glucose readings. Modification of IADPSG criteria would reduce perceived ‘overdiagnosis’ and improve LGA risk-assessment.