Oral glucose tolerance test and glucose challenge test in pregnancy
How the 75 g pregnancy OGTT is done and read against the ADIPS 2025 thresholds, why the 50 g glucose challenge ("polycose") test isn't used in Australia, sample handling errors, HbA1c and fasting glucose as alternatives, and worked results.
Tier 1Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- The 75 g pregnancy OGTT (fasting, 1 hour and 2 hours) is the diagnostic test for gestational diabetes (GDM) in Australia and New Zealand. One abnormal value makes the diagnosis.
- ADIPS 2025 thresholds: fasting 5.3, 1 hour 10.6, 2 hours 9.0 mmol/L. Overt diabetes is fasting 7.0 or more, 2 hours 11.1 or more, or HbA1c 48 mmol/mol or more.
- The 50 g glucose challenge test (GCT, the "polycose" test) is a non-fasting screen followed by a 100 g diagnostic test. It belongs to the US two-step approach and isn't recommended here.
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Sources
- Australasian Diabetes in Pregnancy Society (ADIPS) 2025 consensus recommendations for the screening, diagnosis and classification of gestational diabetesAU/NZSweeting A, Hare MJL, de Jersey SJ, et al. Med J Aust 2025;223(3):161-167, 2025 (current, checked November 2026)
- Therapeutic Guidelines: Diabetes (gestational diabetes)AU/NZTherapeutic Guidelines Limited
- Diagnostic criteria and classification of hyperglycaemia first detected in pregnancyWorld Health Organization, 2013
- Diabetes in pregnancy: management from preconception to the postnatal period (NG3)National Institute for Health and Care Excellence, 2015, updated 2020
- Standards of Care in Diabetes 2026, section 2: Diagnosis and classification of diabetesAmerican Diabetes Association (Diabetes Care 2026;49 Suppl 1), 2026
- International Association of Diabetes and Pregnancy Study Groups recommendations on the diagnosis and classification of hyperglycemia in pregnancyIADPSG Consensus Panel. Diabetes Care 2010;33:676-82, 2010
- Hyperglycemia and adverse pregnancy outcomes (HAPO)HAPO Study Cooperative Research Group. N Engl J Med 2008;358:1991-2002, 2008
- Treatment of gestational diabetes mellitus diagnosed early in pregnancy (TOBOGM)AU/NZSimmons D et al. N Engl J Med 2023;388:2132-44, 2023
- Last updated
- 14 November 2026
What changed
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