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Gestational Diabetes Mellitus (GDM)

Woman testing her blood sugar levels

The National Diabetes Week runs from 12 – 18th July this year and we want to take the opportunity to shed light on Gestational Diabetes Mellitus (GDM).

What is Gestational Diabetes Mellitus (GDM)?

Diabetes is a condition where a person has higher levels of glucose in their blood. Gestational diabetes is a form of diabetes that is diagnosed during pregnancy, and usually goes away after the baby is born. However, some women may continue to have high blood glucose levels after delivery.

What causes GDM?

When we ingest a food or a drink with carbohydrate, this gets broken down into glucose which is absorbed into the bloodstream. The body then uses insulin, a hormone produced by the pancreas, to move glucose from the blood into the body’s cells for it to be used as energy. Essentially, insulin lowers the level of glucose in the blood.

During pregnancy, the body produces more of certain hormones that can block the effects of insulin. Usually the pancreas will increase insulin production but if the pancreas is unable to produce enough insulin to compensate for the block of insulin activity, a higher level of glucose remains in the bloodstream resulting in GDM.

Who is at risk of GDM?

Gestational diabetes is common, between 12% and 14% of pregnant women will develop gestational diabetes. More than 35,000 women are being diagnosed with the condition or its recurrence each year in Australia.

Women at increased risk of GDM include those who are:

  • Age: 40 years or over
  • Ethnicity: Aboriginal and Torres Strait Islander, Polynesian, Chinese, Southeast Asian, Middle Eastern or Indian
  • Family history: type 2 diabetes or gestational diabetes
  • Weight: Above the healthy weight range or gained weight too rapidly in the first half of pregnancy
  • History of elevated blood glucose levels: for example GDM during previous pregnancies
  • Previously given birth to a large baby (weighing more than 4.5kg)
  • Polycystic Ovary Syndrome
  • Medications: taking antipsychotic or steroid medications

Gestational diabetes may also occur in women with no known risk factors.

How is GDM diagnosed?

All pregnant women should be tested for gestational diabetes. This routine screen is usually performed at 26-28 weeks of pregnancy (except for women who already have diabetes). However, women who are at higher risk may be tested earlier in their pregnancy.

Gestational diabetes is diagnosed using an oral glucose tolerance test (OGTT) conducted at a pathology lab. The steps include:

  1. Fasting overnight before having this test
  2. Blood taken right at the start to check for fasting blood glucose level
  3. After this, the pregnant woman will be given a sugary drink containing 75g of glucose
  4. A blood test will be taken an hour later
  5. A repeat blood test taken two hours later

However during current Covid-19 pandemic,

  • if a woman is currently positive for COVID-19, symptomatic or in isolation awaiting test results, any GDM testing should be delayed until after that period
  • For patients where pathology services can meet social distancing requirements:
    • A standard OGTT is performed
  • For patients where pathology services are unable to meet social distancing requirements, the following advice should apply:
    • For patients with identifiable risk factors for GDM in early pregnancy, an HbA1c cut off of 5.9% should be considered diagnostic of GDM
    • Women with previous GDM could be considered as having GDM and commence home blood glucose monitoring from time of diagnosis. Alternatively they can undergo screening as below
    • All other women should have a fasting blood glucose at 2428 weeks
      • Glucose >=5.1mmol/L: assumed GDM
      • Glucose <4.7 mmol/L: no GDM
      • Glucose 4.7-5.1mmol/L: a 2-hour OGTT should be performed

What to do after being diagnosed?

For many women, being diagnosed with gestational diabetes can be upsetting. However, it is important to remember that the majority of women with gestational diabetes have a healthy pregnancy, normal delivery and a healthy baby.

The management of GDM involves healthy eating, regular physical activity and monitoring and maintaining of blood glucose levels within the target range throughout pregnancy. For some women, medications in the form of tablet or insulin injections may be required.

Managing diabetes is a team effort involving the woman, her family and health professionals. Some of the health professionals that may form part of a diabetes health care team include:

  • obstetricians
  • midwives
  • endocrinologists
  • credentialled diabetes educators
  • accredited practising dietitians
  • accredited exercise physiologists/physiotherapist
  • GPs

Will GDM harm me and my baby?

Gestational diabetes does pose some risks for the mother and her baby if it is not well managed. For instance, a mother with GDM is at a higher risk of preeclampsia (high blood pressure during pregnancy) and her baby might get too big making delivery difficult or earlier than expected. But if the advice of the doctor and the health team is followed, this would help reduce the risk of complications and increase the likelihood of a straightforward pregnancy and birth.

What kinds of food should I eat to keep me and my baby healthy?

Most women can manage their gestational diabetes by following a healthy meal plan, gaining only the recommended amount of weight and getting some regular exercise.

A dietitian can help provide a healthy meal plan which involves regular meal pattern and appropriate portion sizes.

In order to get all the vitamins and minerals you and your baby need, you should try to eat food rich in vitamins and nutrients from different sources every day. Aim for:

  • Wholegrains and low glycaemic index starches
  • An array of colourful vegetables (5 serves) and fruits (2 serves) a day
  • Lean and iron rich protein such as lentils, pulses, tofu and nuts, meat, eggs, chicken, fish
  • Low fat dairy products such as milk, cheese and yogurt
  • Adequate fluids up to 2 litres/day unless your health team has advised otherwise
  • Eat less foods which are high in fat, salt and refined sugar

Consider having small frequent meals such as 3 meals and 3 snacks a day. By spreading the food out over the day, you will be better able to keep your blood glucose in the target range while managing your hunger.

How does exercise help with managing GDM?

Physical activity of any intensity be it light or moderate, as long as it gets your blood circulating and muscle moving, this can helps to lower your blood glucose. However, please check with your obstetrician and/or physiotherapist if you are planning to start a new activity.

How will GDM impact the delivery of my child?

If GDM is well managed and there are no other problems, most women will go “full term” and give birth naturally.

If there are concerns about your baby growing too large, you will generally be offered an additional growth scan around 34-36 weeks, and depending on your baby’s estimated size, the most suitable mode of birth will be discussed with you by your caring obstetrician. 

What happens after delivery?

Exposure to high blood glucose in the womb predisposes a child to a high risk of becoming overweight or obese, associated with the development of T2DM. Maternal blood glucose levels can also impact the initial stability of a newborn baby’s blood glucose, which is why your baby will have blood sugar monitoring throughout the initial day or so. Your midwife can help to explain this to you further, discuss how it can be managed and speak with you about antenatal preparations that can be made.

In most women, blood glucose go back to normal as soon as the baby is born. In those women where diabetes does not go away, it means they probably had diabetes before they became pregnant but likely did not know it. Women who have had gestational diabetes are at high risk of recurrence with future pregnancies and the development of type 2 diabetes later in life. Approximately half of women with a history of GDM go on to develop type 2 diabetes within five to ten years after delivery.

Between 6 – 12 weeks after your baby is born you will need to return to the clinic for a blood test to determine if you have developed pre-diabetes or diabetes. If you have not, you are still encouraged to have an annual screen for diabetes.

Healthy eating and regular physical activity will help reduce the risk of being overweight and in turn, prevent diabetes. Hence, it is encouraged for the mother and child to maintain these positive dietary and lifestyle changes for the long term.

If you have been diagnosed with GDM, here at Create Health we have a comprehensive and collaborative team ready to help support you. Along with your obstetrician to oversee your pregnancy, both our in-house dietician (Janet Yong) and our practice midwife (Michelle Sullivan) are qualified Diabetes Educators and can assist you in answering your questions and guiding you further.


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