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How is diabetes in pregnancy diagnosed?

Pregnant women should be tested for gestational diabetes at 24-28 weeks gestation


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Every pregnant woman is at risk of developing gestational diabetes, so it is recommended that all pregnant women are screened using a glucose tolerance blood test at 24-28 weeks’ gestation.

There are some women who are at a higher risk of developing gestational diabetes. For women who have previously had diabetes during pregnancy, they are at a higher risk of developing gestational diabetes again.

These women who are at a much higher risk, should be screened before becoming pregnant, at 12 weeks’ gestation and again at 24-28 weeks if not previously diagnosed.



What are the risk factors for developing gestational diabetes?

High risk factors for developing gestational diabetes include:

  1. women aged 25 years or over
  2. family history of type 2 diabetes
  3. family history of gestational diabetes, especially from a first-degree relative like a mother or sister
  4. being overweight or obese
  5. had gestational diabetes in a previous pregnancy
  6. multiple pregnancies in the past
  7. have previously given birth to a large baby (weighing more than 4.5kgs)
  8. gained weight rapidly during the first trimester of pregnancy
  9. a previous diagnosis of Polycystic Ovary Syndrome
  10. of non-Caucasian descent, including African-American, Aboriginal or Torres Strait Islander, Melanesian, Polynesian, Chines, Southeast Asian, Middle Easter or Indian background

You can read more about the risk factors for gestational diabetes for more information.



How is gestational diabetes diagnosed?

All women should be tested for gestational diabetes at weeks 24-28 gestation, which is during your second trimester. You are at a high risk of gestational diabetes if you are obese at the beginning of your pregnancy; have previously had gestational diabetes; or a close family member (i.e. mother, father, or sibling) has diabetes. If you are at a higher risk, your doctor may screen you earlier for gestational diabetes.

A pregnancy oral glucose tolerance test involves:

  • fasting overnight (for at least 8 hours)
  • initial blood test to test fasting glucose levels
  • drinking a syrupy glucose solution containing 75 grams of glucose
  • have a blood test an hour after drinking the glucose solution
  • have a final blood test two after drinking the glucose solution

Typically, a blood glucose reading below 7.8mmol/L (140mg/dL) is considered to be normal.



What are the diagnostic criteria for gestational diabetes?

An elevation in blood glucose levels are diagnostic at either the fasting, 1 hour or 2-hour test. You only need one test to show abnormal blood glucose readings higher than normal values, to be diagnosed with gestational diabetes.

Diagnostic criteria for Gestational Diabetes Mellitus
Fasting glucose 1 hour glucose 2 hour glucose
5.2 mmol/L or more 10.0 mmol/L or more 8.5 mmol/L or more
92 mg/dL or more 180 mg/dL or more 153 mg/dL or more


Read about how diabetes is diagnosed for more information.



What are the targets glucose levels in gestational diabetes?

Currently, there have been no studies that have defined the optimal glycaemic targets for women with gestational diabetes. Further research is required to determine optimal blood glucose targets.

Below are suggested from the Australasian Diabetes in Pregnancy Society targets for women with gestational diabetes:

  • fasting blood glucose: 5.0mmol/L or less
  • 1 hour after eating a meal: 7.4mmol/L or less
  • 2 hours after eating a meal: 6.7mmol/L or less

Your specific blood glucose targets may be set by your doctor.

The Hb A1c targets for women who already have type 1 diabetes or type 2 diabetes, can be found in our article ‘what is the Hb A1c test’.



What should I do next?

If you experience any symptoms of gestational diabetes or you have risk factors for developing gestational diabetes, it is important to be tested at 24-28 weeks gestation. Some people are at higher risk than others. If you are 25 years or older or have other risk factors for diabetes, you may require testing earlier in pregnancy. By diagnosing and treating gestational diabetes, it means you can decrease the risk of developing or delay any further health complications of gestational diabetes. These complications can affect both you and your child later in life, for example you are both at risk of developing type 2 diabetes. It is important to know that diagnosing diabetes should not rely solely on using a Hb A1c test.

Once you learn what your gestational diabetes status is, or if you already have gestational diabetes, the next most important step is to become educated. You can join the Gestational Diabetes Program to help you learn how to manage gestational diabetes and improve health outcomes for you and your child. The program is personalised and tailored, giving you more of the content that you want. The program also helps you to stay motivated and teaches you what changes you need to make.




Interested in more information on type 1 diabetes?

Follow the links below to learn more about type 1 diabetes.

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Monitoring Gestational Diabetes

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Treating
Gestational Diabetes

My Health Explained has easy to use tools to help track your progress

Tools for Gestational Diabetes

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Preventing Gestational Diabetes