gestational diabetes
Gestational Diabetes - Screening Tests
GDM = Gestational Diabetes Mellitus
OGTT = Oral Glucose Tolerance Test
All women (without risk factors) have a routine OGTT test at 24–28 weeks gestation.
If you have risk factors, you GP will advise to
1. Have a fasting glucose test at diagnosis of your pregnancy and
2. Have an OGTT prior to 12 weeks gestation.
If this is a normal result, you will then go on to have repeat testing at 24–28 weeks gestation.
Moderate risk factors for GDM
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Ethnicity: Asian, Indian subcontinent, Aboriginal, Torres Strait Islander, Pacific Islander, Maori, Middle Eastern, non‐white African
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BMI 25 – 35 kg/m2
High risk factors for GDM
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Previous GDM
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History of known previously elevated blood glucose level
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Maternal age ≥40 years
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Family history of Diabetes (1st degree relative with diabetes or a sister with GDM)
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BMI > 35
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Previous baby with birth weight > 4500 g or > 90th centile
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Polycystic ovarian syndrome
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Medications: corticosteroids, antipsychotics
In early pregnancy (before 24 weeks), the 2-hr OGTT is now only routinely recommended for women who have had GDM before in another pregnancy or for women whose HbA1c test is borderline.
Preparing for the OGTT
Patient preparation instructions
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Ensure you maintain a normal diet with an adequate carbohydrate content and your usual physical activity at least 3 days prior to your test.
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Ensure you have had nothing to eat or drink (other than plain water) overnight for 8 – 12 hours prior to coming in for your test. DO NOT fast for longer than 15 hours, as this may affect your results.
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Water is allowed anytime overnight. Please maintain adequate level of plain water consumption to ensure good hydration.
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Upon arrival at the collection centre, make the pathology collection staff aware of the test you require. This doesn’t mean they will attend to you next, but they are then able to manage the flow of patients with your test in mind.
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Smoking, food or drinks are not permitted during the test.
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During the test, you will have your blood taken 3 times over the 2 hours.
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After the fasting blood sample is taken, you will be given a glucose drink.
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Please finish the drink in a maximum of 5 minutes.
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You will then have your blood collected 1 hour and then 2 hours after the drink.
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Diagnosed with GDM ?
A diagnosis of GDM is made if one or more of the following glucose levels are elevated (2025 Update)
Fasting glucose ≥ 5.3 mmol/L
1‐hr glucose ≥ 10.6 mmol/L
2‐hr glucose ≥ 9.0 mmol/L
If you are diagnosed with GDM, your doctor will talk to you about developing an individualised management plan for your pregnancy. Your doctor may recommend a referral to a Diabetes Educator to join your Care Team.
Type 2 Diabetes
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Type 2 diabetes can’t be diagnosed during pregnancy and requires confirmation after pregnancy
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Instead the term “Overt Diabetes in Pregnancy” is used.
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The criteria for overt Diabetes in Pregnancy are:
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HbA1c ≥ 6.5%,
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Fasting glucose ≥ 7.0 mmol/L, OR
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2-hr glucose ≥ 11.1 mmol/L
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These are the same thresholds for the diagnosis of type 2 diabetes in people who are not pregnant.
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Some, but not all, women with overt Diabetes in Pregnancy will actually have undiagnosed diabetes that was there before the pregnancy but hadn’t been picked up.
Blood Sugar Targets
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Your targets for your blood sugars may be individualised & may vary between services
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General targets are
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Fasting BGL target of ≤5.2 mmol/L
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Post-meal targets of
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≤7.4 mmol/L at one hour
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≤6.7 mmol/L at two hours
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