Poster Presentation Australasian Diabetes in Pregnancy Society Annual Scientific Meeting 2016

Gestational Diabetes Mellitus: Should we measure 1-hour glucose levels? (#124)

Hong Lin Evelyn Tan 1 , Judy Luu 1 2 , Amanda Caswell 2 3 , John Attia 2 , Shamasunder Acharya 1 2
  1. Department of Endocrinology and Diabetes, John Hunter Hospital, New Lambton, NSW, Australia
  2. School of Medicine and Public Health, University of Newcastle, Newcastle, NSW, Australia
  3. Hunter Medical Research Institute, Newcastle, NSW , Australia

Introduction: The optimal diagnostic criteria for gestational diabetes (GDM) continue to be widely debated, with guideline recommendations based on statistical postulations of adverse outcomes from the Hyperglycaemia and Adverse Pregnancy Outcomes (HAPO) study1. Only one abnormal glucose reading is required for diagnosis of GDM (fasting glucose ≥5.1mmol/L; 1-hour glucose ≥10mmol/L; or 2-hour glucose ≥8.5mmol/L). Baseline and 2-hour glucose readings have been commonly used for antenatal oral glucose tolerance tests (OGTT), but the clinical utility of 1-hour glucose levels remains largely unknown. There has been variable adoption of this additional test due to increased resource strain with unclear benefits of improved pregnancy outcomes.

Hypothesis: Women with normal OGTT levels at baseline and 2 hours, but elevated 1-hour glucose have increased perinatal complications.

Methods: A total of 2897 antenatal 75g OGTTs were collected from a single laboratory over an 18-month period. Maternal data and perinatal outcomes were analysed for women diagnosed with GDM through an isolated raised 1-hour glucose level. Receiver operating curves (ROC) were used to determine the best cut off values for using 1-hour glucose to predict elevated 2-hour glucose (≥8.5mmol/L) in women with normal fasting glucose (<5.1mmol/L).

Results: Of 263 GDM positive women with elevated 1-hour glucose, 107 (40.7%) had normal fasting and 2-hour glucose. These pregnancies were not significantly associated with increased risk of perinatal complications, although all odds ratio estimates were greater than 1. Using an area under the ROC curve from the logistic model, a 1-hour glucose of 8.2mmol/L was a strong predictor of 2-hour glucose ≥8.5mmol/L, using a predicted probability of 0.035, sensitivity 84.5%, specificity 80.6%, positive likelihood ratio 4.36 and negative likelihood ratio of 0.19.

Conclusion: Routine screening of 1-hour glucose during OGTT for diagnosis of GDM may not be necessary, as a cut off of ≥10mmol/L does not result in significant reduction in perinatal outcomes. With the advent of universal screening, cost savings may be substantial if only one test post glucose challenge is performed. A 1-hour test, instead of 2-hour, with more stringent diagnostic criteria of ≥8.2mmol/L may be considered, with benefits including reduced time in the laboratory, and improved resource utilisation.

  1. Coustan DR, Lowe LP, Metzger BE, et al. The Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study: paving the way for new diagnostic criteria for gestational diabetes mellitus. Am J Obstet Gynecol 2010;202:654.e1-6.