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. 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. 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.
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'.
History and exam
Key diagnostic factors
- presence of risk factors (usually asymptomatic)
Other diagnostic factors
- fetal macrosomia in a previous pregnancy
- elevated BMI
- previous gestational diabetes
- previous macrosomic baby
- family history of diabetes mellitus
- non-white ancestry
- advanced maternal age (>40 years)
- polycystic ovarian syndrome (PCOS)
1st investigations to order
- oral glucose tolerance test (OGTT)
Investigations to consider
- random blood (plasma) glucose
- fasting plasma glucose (FPG)
fasting plasma glucose ≥7 mmol/L (or 6 to 6.9 mmol/L if large fetus/polyhydramnios)
fasting plasma glucose <7 mmol/L without large fetus/polyhydramnios
- Type 1 diabetes
- Type 2 diabetes
- Standards of medical care in diabetes - 2022
- Diabetes in pregnancy: management from preconception to the postnatal period
Diabetes that develops in pregnancy (gestational diabetes)
Diabetes: what can I do to keep healthy?More Patient leaflets
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