Gestational diabetes: screening, diagnosis, management

It is Tuesday clinic and the GP has sent a 33-year-old at 26 weeks with a fasting glucose of 5.4 mmol/L. Two years ago that number was normal; today it is a diagnosis. Nothing about her has changed — the threshold has. That single sentence is the whole examinable tension in this topic, and the candidate who can argue it from both sides walks out of the station with marks.^[1][7]

Overview and definition

Gestational diabetes is a statement about detection, not about aetiology. It means hyperglycaemia first found in pregnancy that does not reach the criteria for overt diabetes.^[1][16]

• Some of these women have transient pregnancy-induced glucose intolerance that resolves at birth.
• Some have pre-existing beta-cell dysfunction that pregnancy has simply unmasked.
• A few have undiagnosed type 2 diabetes, monogenic diabetes, or early type 1 diabetes wearing a GDM label.^[1][16]

That heterogeneity is why the postpartum test matters as much as the antenatal one, and why "her GDM resolved" is never a discharge diagnosis until you have proved it.^[1][15]

References20ShowHide

1. [1]Sweeting A, Hare MJ, de Jersey SJ, et al. Australasian Diabetes in Pregnancy Society (ADIPS) 2025 consensus recommendations for the screening, diagnosis and classification of gestational diabetes. Med J Aust, 2025.PMID 40544364
2. [2]Metzger BE, Lowe LP, Dyer AR, et al. Hyperglycemia and adverse pregnancy outcomes. N Engl J Med, 2008.PMID 18463375
3. [3]Metzger BE, Gabbe SG, Persson B, et al. International association of diabetes and pregnancy study groups recommendations on the diagnosis and classification of hyperglycemia in pregnancy. Diabetes Care, 2010.PMID 20190296
4. [4]Crowther CA, Hiller JE, Moss JR, et al. Effect of treatment of gestational diabetes mellitus on pregnancy outcomes. N Engl J Med, 2005.PMID 15951574
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8. [8]Crowther CA, Samuel D, Hughes R, et al. Tighter or less tight glycaemic targets for women with gestational diabetes mellitus for reducing maternal and perinatal morbidity: A stepped-wedge, cluster-randomised trial. PLoS Med, 2022.PMID 36074760
9. [9]Hillier TA, Pedula KL, Ogasawara KK, et al. A Pragmatic, Randomized Clinical Trial of Gestational Diabetes Screening. N Engl J Med, 2021.PMID 33704936
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14. [14]Committee on Practice Bulletins-Obstetrics ACOG Practice Bulletin No. 190: Gestational Diabetes Mellitus. Obstet Gynecol, 2018.PMID 29370047
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18. [18]Roberts L, Lin L, Alsweiler J, et al. Oral dextrose gel to prevent hypoglycaemia in at-risk neonates. Cochrane Database Syst Rev, 2023.PMID 38014716
19. [19]Farrant MT, Williamson K, Battin M, et al. The use of dextrose/insulin infusions during labour and delivery in women with gestational diabetes mellitus: Is there any point? Aust N Z J Obstet Gynaecol, 2017.PMID 27531282
20. [20]Gordon HG, Shub A, Walker SP, et al. Maternal Diabetes, Fetal Growth, and Stillbirth Risk: A Population-Wide Retrospective Cohort Study From Victoria, Australia. Diabetes Care, 2025.PMID 40902109