Gestational diabetes mellitus (sometimes referred to as GDM) is a form of diabetes that occurs during pregnancy. Most women will no longer have diabetes after the baby is born. However, some women will continue to have high blood glucose levels after delivery. It is diagnosed when higher than normal blood glucose levels first appear during pregnancy.

Gestational diabetes is the fastest growing type of diabetes in Australia, affecting thousands of pregnant women. It is usually occurs around the 24th to 28th week of pregnancy. All pregnant women should be tested for gestational diabetes at 24-28 weeks of pregnancy (except those women who already have diabetes). Women who have risk factors for gestational diabetes should be tested earlier in their pregnancy.

Who is at increased risk of gestational diabetes?

Women at increased risk of developing gestational diabetes include those who:

• have had GDM in a previous pregnancy
• are older, especially aged 40 years or over
• have a family history of type 2 diabetes or a first-degree relative (mother or sister) who has had gestational diabetes
• are above the healthy weight range
• have previously had elevated blood glucose levels
• are First Nations women
• are from an African, Melanesian, Polynesian, South Asian, Chinese, Southeast Asian, Middle Eastern, Hispanic and South American backgrounds
• have Polycystic Ovary Syndrome
• have previously given birth to a large baby (weighing more than 4.5kg)
• are currently taking some types of anti-psychotic or steroid medications.

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

How is gestational diabetes diagnosed?

Gestational diabetes is diagnosed using an oral glucose tolerance test (OGTT). This is done at a pathology lab. You will need to fast overnight before having this test. Blood will be taken to check your fasting blood glucose level. After this, you will be given a sugary drink and have your blood tested one and two hours later. You will be asked to sit and wait between tests. If your blood glucose level is above the normal range at your fasting, one- or two-hour test, you have gestational diabetes.

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 treatment is a healthy eating plan, regular physical activity and monitoring and maintaining blood glucose levels in the target range while you are pregnant. Read more about managing gestational diabetes.

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 endocrinologists, obstetricians, credentialled diabetes educators, accredited practising dietitians, accredited exercise physiologists, GPs and midwives.

Risks of developing type 2 diabetes

While maternal blood glucose levels usually return to normal after birth, there is an increased risk of the woman developing type 2 diabetes in the future. The baby may also be at risk of developing type 2 diabetes later in life.

Depending on your risk factors, you will also need to be tested for type 2 diabetes again every one to three years. Ask your doctor for more information. You can find more information about reducing your risk of type 2 diabetes here.

What causes gestational diabetes?

In pregnancy, the placenta produces hormones that help the baby grow and develop. These hormones also block the action of the woman’s insulin. This is called insulin resistance. Because of this insulin resistance, the need for insulin in pregnancy is 2 to 3 times higher than normal. If you already have insulin resistance, then your body may not be able to cope with the extra demand for insulin production and the blood glucose levels will be higher resulting in gestational diabetes being diagnosed.

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