Gestational diabetes mellitus

Gestational diabetes mellitus (GDM) develops during pregnancy and is usually diagnosed following assessment for risk factors followed by elevated plasma glucose levels on testing.

Goal of therapy is to achieve maternal glucose levels that are as close to normal as possible in order to avoid fetal macrosomia and complications.

Initial therapy for GDM is usually dietary modification, unless women have marked elevated glucose levels, which will require immediate initiation of insulin (with or without metformin). If acceptable glucose levels cannot be maintained with diet alone, therapy is typically stepped up to add metformin and then insulin.

Maternal postnatal testing for diabetes or impaired glucose tolerance is performed at 6 to 13 weeks following delivery and annually thereafter.

The risk for recurrence of GDM in subsequent pregnancies or progression to type 2 diabetes is high and all women with a history of GDM should be offered additional screening for cardiovascular risk factors as well as support for weight management and diabetes prevention.

GDM is defined as hyperglycaemia in pregnancy that is below diagnostic thresholds for diabetes.[1]Metzger BE, Gabbe SG, Persson B, et al; International Association of Diabetes and Pregnancy Study Groups Consensus Panel. International association of diabetes and pregnancy study groups recommendations on the diagnosis and classification of hyperglycemia in pregnancy. Diabetes Care. 2010 Mar;33(3):676-82. http://care.diabetesjournals.org/content/33/3/676.long http://www.ncbi.nlm.nih.gov/pubmed/20190296?tool=bestpractice.com [2]Diagnostic criteria and classification of hyperglycaemia first detected in pregnancy: a World Health Organization Guideline. Diabetes Res Clin Pract. 2014 Mar;103(3):341-63. https://www.doi.org/10.1016/j.diabres.2013.10.012 http://www.ncbi.nlm.nih.gov/pubmed/24847517?tool=bestpractice.com The precise diagnostic criteria remain a subject of debate. Guidelines differ in their recommendations on the stage of pregnancy when GDM can be diagnosed. The World Health Organization criteria state that it can be diagnosed at any time in pregnancy, whereas the American Diabetes Association limits the definition to hyperglycaemia that is first detected after the first trimester.[3]American Diabetes Association. Standards of medical care in diabetes - 2022. Diabetes Care. 2022 Jan;45(1 suppl):S1-255. https://diabetesjournals.org/care/article/45/Supplement_1/S254/138913/17-Diabetes-Advocacy-Standards-of-Medical-Care-in In the UK, the National Institute for Health and Care Excellence does not specify a timeframe but recommends that women should be assessed for risk factors at their booking appointment and those with risk factors should be tested for GDM, with the timing of the testing dependent on which risk factor(s) are present.[4]National Institute for Health and Care Excellence. Diabetes in pregnancy: management from preconception to the postnatal period. Dec 2020 [internet publication]. https://www.nice.org.uk/guidance/ng3

In practice, GDM is most often recognised at 24 to 28 weeks of gestation, based on an abnormal glucose tolerance test.

This topic covers women whose hyperglycaemia is first detected during pregnancy. For management of pregnancy in women with pre-existing diabetes, see our topics 'Type 1 diabetes in adults' and 'Type 2 diabetes in adults'.

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