Understanding GDM

Written by Natasha Leader, Accredited Practising Dietitian & Credentialled Diabetes Educator

Last updated July 2011.

What is gestational diabetes?

Gestational diabetes mellitus (GDM) is a (usually) temporary form of diabetes that occurs during pregnancy. It happens when the hormones made by the placenta during pregnancy make it harder for insulin to work. Insulin is a hormone that helps process your food and keeps your blood glucose level stable. If you can’t make enough insulin your blood glucose levels will rise. High blood glucose levels can cause the baby to put on too much weight. This can impact on the baby’s wellbeing and your delivery and can affect the baby’s health later in its life.

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How common is gestational diabetes?

17,000 pregnant women are diagnosed each year in Australia (around 5-8% of all pregnancies) and the risk is much higher in certain ethnic populations.

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Why test for gestational diabetes? What are the symptoms?

Many pregnant women don’t experience symptoms of diabetes (blood glucose ‘highs’ or ‘lows’) and would otherwise go undiagnosed. It’s important to test for gestational diabetes in order to prevent complications during pregnancy and childbirth.

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Who is most at risk of developing gestational diabetes?

Women most at risk are those who:

  • are over 35 years of age
  • have a family history of type 2 diabetes
  • are overweight or obese
  • are of Aboriginal, Torres Strait Islander, Indian, Asian, Middle Eastern, Mediterranean or Polynesian ethnic background
  • have had gestational diabetes during previous pregnancies
  • have previously had a baby weighing over 4kg
  • have polycystic ovarian syndrome (PCOS)
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How is gestational diabetes diagnosed?

Generally you will be screened for diabetes at around 28 weeks in your pregnancy. Most women will have a Glucose Tolerance Test (GTT).

The GTT is a 2 hour test, and will be done at your hospital or a pathology centre. After fasting for 10 hours, the following will happen:

  • You will have a blood sample taken on arrival. This is your fasting blood glucose level and provides a baseline reading.
  • Next, you will be asked to drink a very sweet liquid containing 75g of glucose.
  • Following this, blood samples will be collected at timed intervals of 1 and always 2 hours. The results of these samples will show how effective your body’s insulin is at processing the glucose.

If you’ve had gestational diabetes in your previous pregnancies or have many risk factors for developing GDM, you may be tested earlier in your pregnancy.

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Why did I get gestational diabetes?

For the moment, there is no clear answer. You can still develop gestational diabetes without having any of the usual risk factors. That’s why it’s recommended all pregnant women get tested.

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My glucose tolerance test result is only a little above normal. Do I really have gestational diabetes?

The level of blood glucose is only an indicator of potential problems. The higher the level, the higher the risk. Also, blood glucose levels tend to rise as the pregnancy progresses so both you and your baby are still at risk if you don’t start managing your blood glucose levels.

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Why aren’t women tested earlier than week 28?

It is less common for women to develop gestational diabetes before this time. At around 28 weeks gestation your hormone levels are much higher than they were earlier in the pregnancy and are more likely to interfere with your body’s ability to process glucose. Diagnosis at this stage still allows time to manage and control your baby’s growth and wellbeing.

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Will I have to inject insulin?

Even when you follow the diet carefully and include regular activity you may still find that your glucose levels are still too high. This doesn’t mean you are doing anything wrong. It just means you still aren’t able to make enough insulin to process what you are eating.

Between 20-60% (depending on the care provider) of women with gestational diabetes will need insulin injections to control their diabetes. This is considered the safest way to manage the blood glucose levels. Please note, it is not safe to avoid eating to control your blood glucose levels.

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What are the risks of gestational diabetes to my baby?

If blood glucose levels aren’t managed during pregnancy your baby can gain too much weight, in particular body fat around its belly. A large baby makes birth more difficult and increases the chance of interventions during labour. Managing blood glucose levels during pregnancy can significantly reduce these risks.

There is also an increased risk of childhood obesity in babies who have a high birth weight. Obesity further increases the risk of developing health problems such as high blood pressure, heart disease and diabetes later in life.

Babies may have problems with low blood glucose levels at birth and some babies will not receive enough nutrition from the placenta if there are problems with your blood pressure being high. Women with gestational diabetes are more likely to have problems with high blood pressure and pre-eclampsia.

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Will my baby be born with diabetes?

No, a mother can’t directly pass on diabetes to her baby through having gestational diabetes. However children of women with a history of GDM are at higher risk of developing type 2 diabetes later in life.

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Will my baby need special treatment at birth?

Managing diabetes throughout pregnancy and reducing the possibility of intervention during labour can reduce the chance of your baby requiring special treatment after delivery (eg. needing to be taken to a special care nursery.) It’s a good idea to talk about these things with your midwife, doctor or obstetrician beforehand.

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Can I breastfeed my baby after having gestational diabetes?

Having gestational diabetes won’t impact your ability to breastfeed. In fact early breastfeeding (within half an hour of birth) can help your baby maintain normal levels of blood glucose. Your baby will have a heel prick blood test several times during its first day to test for low blood glucose levels. Breastfeeding may also reduce your baby’s risk of developing diabetes later in life.

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Does gestational diabetes go away?

Yes, in most cases gestational diabetes will go away as soon as your baby and placenta are delivered. However you now have up to a 50% chance of developing type 2 diabetes within a decade from your pregnancy. The best way to avoid and delay the onset of type 2 diabetes is through regular activity, healthy diet and weight control.

If you are in Australia, and have Medicare cover you should register your details with the National Gestational Diabetes Register. This register is run by the National Diabetes Services Scheme (NDSS) and provided you keep your contact information updated with them, you will receive vital follow-up reminders on when to get tested again for GDM post-pregnancy. This is important for your long-term health and also if you are planning further pregnancies.

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Can gestational diabetes turn into type 2 diabetes?

Anyone who has had gestational diabetes has up to a 50% risk of developing type 2 diabetes within a decade of the pregnancy. The risk of developing type 2 diabetes is significantly influenced by your lifestyle. Ensuring regular activity and controlling your body weight can help reduce your risk of developing diabetes.

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I've been diagnosed with gestational diabetes. What should I do now?

Get as much support and information as you can to help you and your baby have the best possible outcome.

  • If you are in the public hospital system you will mostly likely see an endocrinologist and/or diabetes educator and probably a dietitian. If you are in private care you may be referred to a public hospital that already has an established diabetes clinic or you may be referred privately to an endocrinologist and/ or diabetes educator and/ or dietitian. It’s important to feel comfortable with the level of care you are getting and get further help if you need it.
  • Make exercise a part of your day from the day of diagnosis. You need to keep active to maintain healthy blood glucose levels. Be realistic and choose activities that fit in with your workday, lifestyle, kids, partner, ability and budget. It is recommended you undertake 30 minutes of activity each day unless your obstetrician has advised you not to exercise. High intensity exercise is not needed, nor recommended. You may like to try splitting the 30 minutes across the day like walking for 10-15 minutes after 2-3 of your meals.
  • Visit our ‘Eating Well’ section and start using GestationalDiabetesRecipes regularly to help you plan and cook delicious meals that work with your recommended diet. Share your story with the community here and learn more about living positively with gestational diabetes.
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