Gestational Diabetes: The Causes, Risks and Symptoms

Gestational diabetes mellitus – also known as GDM, is diabetes which can occur during pregnancy.

Many women who’ve been diagnosed with GDM won’t have diabetes after their baby is born, though some continue to have high levels of blood glucose and need treatment. Most women who are diagnosed with GDM have a normal pregnancy, labour and baby.

It’s important that GDM is monitored and controlled, because risk factors increase when blood sugar levels remain high.

What causes gestational diabetes?

During pregnancy, special hormones produced by the placenta help the baby to grow and develop. These hormones can also block the action of the pregnant mother’s insulin. Insulin is a special hormone which helps to stabilise blood sugar levels.  When there is insulin resistance, sugar cannot pass as easily from the blood and into the cells where it’s needed for energy.  

When the pregnancy is over, blood glucose levels usually return to normal and gestational diabetes resolves.  However, insulin resistance during pregnancy increases the risk of developing type 2 diabetes in later life.

Risks of Gestational Diabetes

Diabetes during pregnancy can increase the risk of miscarriage and complications in the developing baby.  Risk factors increase when blood sugar levels are not within a normal range. Premature birth or, having a baby with a large birth weight (macrosomia) is more common.

There is also an increased risk of other complications during pregnancy - excessive weight gain, maternal high blood pressure and pre-eclampsia. Labour and birth complications are also more likely.

Babies of mothers who had GDM are at an increased risk of developing type 2 diabetes when they are older.

Planning and preparing for pregnancy and careful management of diabetes during pregnancy, has been shown to reduce the risk of health problems and improve pregnancy outcomes for women with diabetes.

Women at higher risk of developing GDM

1. Have a history of blood glucose problems in the past.
2. Are overweight or obese.
3. Are aged 40 years or older.
4. Have gained a lot of weight during their pregnancy, particularly in the first two trimesters.
5. Are of Aboriginal or Torres Strait Islander descent.
6. Are from Melanesian, Polynesian, Chinese, Middle Eastern, Indian or Southeast Asian backgrounds.
7. Have a family history of type 2 diabetes or, a mother or sister who had GDM.
8. Previous history of GDM themselves.
9. Have previously had a large baby e.g. >4.5 kgs.
10. Have polycystic ovarian syndrome (POS).
11. Are taking some types of steroid or anti-psychotic medications.

How likely am I to get GDM?

Around 12-14% of pregnant women develop GDM. Most are diagnosed between weeks 24-28 of pregnancy when they have a glucose tolerance test (GTT).

To prevent GDM

1. Try to keep within a healthy weight range. Check here for recommendations about BMI.
2. Start your pregnancy at a healthy weight.
3. Keep active with regular exercise.
4. Aim to eat foods which will sustain your hunger and not cause sudden spikes in sugar levels. Whole grains, meat, fish, dairy foods and (some) fruits and vegetables are all good alternatives to sweet treats.
5. Keep a record of your pregnancy weight gain. Don’t become too focused on every kg, but it can be  helpful to be aware of how much gain there’s been since your pre-pregnancy weight.

How would I know if I’ve got Gestational Diabetes?

Some women develop GDM without having any risk factors at all. The first they know that their blood glucose level is higher than normal, is when they have the results of their oral glucose tolerance test (OGTT).

Many women don’t know they have GDM until they’re diagnosed. Sometimes there are no, or minimal, symptoms though an increased thirst and needing to wee more often are characteristic of diabetes.

If you have one or more of the risk factors (above) then you need to be mindful of the possibility. 

How is gestational diabetes diagnosed?

Gestational diabetes is most commonly diagnosed by an oral glucose tolerance test. All women need to have this test between weeks 24-28 weeks of pregnancy. Sometimes maternity care providers recommend earlier testing if a woman has had GDM before or, she is in a risk category.

After fasting overnight, a sample of blood is collected.  Levels of blood glucose are compared with another sample of blood which is taken 1-2 hours after drinking a very sweet liquid. If the result shows the level of blood glucose is higher than the normal range, GDM is suspected.   

What do I need to do if I’m diagnosed?

Try to understand as much as you can about GDM. Read evidence based information and find out what’s relevant to you and your pregnancy.

When first diagnosed, many women are (understandably) anxious about what GDM means. Treatment is most effective when there is a combined approach involving monitoring and maintaining blood glucose levels, eating a healthy and nutritious diet and regular exercise. Without all three factors playing their part, GDM can become uncontrolled. You will need to test your blood sugar level a couple of times each day and keep a record of the readings.

Many women who develop GDM need to take medication which helps to control blood sugar levels. This can be in the form of tablets or injections of insulin.

Most women who are diagnosed with GDM benefit by seeing a dietician. These are health professionals who are able to give advice about what foods to eat, when to eat and how to manage a diet which provides all the essential nutrition without high levels of carbohydrates. Similar information can be found in our Pregnancy Eating Guide which has been written by industry professionals.

You may also be referred to:

1. An obstetrician and/or endocrinologist who have special expertise in managing pregnancy related complications.
2. A specialist clinic with staff who have special training in GDM.
3. An exercise physiologist may be able to give you insights about exercise.

Remember, keep informed about your choices and the best way of reducing your individual risks.

Written for Nourish Baby by: Jane Barry, Midwife and Child Health Nurse.