Patient Info

Oral Glucose Tolerance Test

Why is it important?

All pregnant women should be tested for diabetes in pregnancy – also known as Gestational Diabetes (GDM). It is important to diagnose GDM because untreated diabetes can harm the health of mother and baby.

What is an oral glucose tolerance test (OGTT)?

OGTT is a blood test used to check how the body processes sugar. It is performed between 24 and 28 weeks of pregnancy, although some women may need to be tested earlier. You need to fast from midnight (water is allowed) and visit a pathology collection centre in the morning. A fasting blood sample will be taken followed by a glucose drink. Two other blood samples will be taken in one and two hours. No food or drink can be consumed during this time. Gestational Diabetes is diagnosed if any of these levels are elevated.

What happens if you have gestational diabetes?

First and foremost, please don’t feel alarmed — you’re not alone. 1 in 5 Australian women are diagnosed with gestational diabetes during pregnancy. It’s a common condition and one that we manage together as a team to support the health of both you and your baby.

If you have Gestational Diabetes, you will be referred to a Diabetes Educator and possibly an Endocrinologist (Specialist Diabetes Doctor) and a Dietician. This is in addition to your regular obstetric reviews. You will be taught how to regularly monitor your blood glucose levels. Most women are able to manage GDM with diet and exercise, but in some cases Insulin may be required.

Further ultrasounds and additional monitoring of the baby may be required later in pregnancy. Timing and mode of birth will depend on multiple factors, including your glucose levels and the wellbeing of your baby.

How can GDM affect the health of the mother?

Untreated GDM also increases the risk to mothers’ health. Some potential risks include:

  • Hypertension and Preeclampsia (pregnancy associated Blood Pressure Problems)
  • Caesarean Section and Instrumental Vaginal Birth
  • Birth Complications eg tissue trauma, haemorrhage
  • Long term Complications – increased risk of Type 2 Diabetes and Heart Disease

How can GDM harm my unborn baby?

If left untreated, GDM can increase the risk of complications for babies during and after pregnancy. Some potential risks include:

  • Macrosomia – Mother’s blood glucose passes through the placenta to the baby. If baby’s blood glucose levels are high, baby will make extra Insulin to bring these high glucose levels down. This can cause the baby to grow larger than normal, which can cause problems with birth.
  • Hypoglycaemia – Babies of mothers with GDM are at an increased risk of low blood sugar levels after birth. This is because these babies stop receiving extra glucose from their mother but temporarily continue producing more Insulin. Fortunately, this can be easily treated with early feeding as well as extra oral or IV glucose if required. If left untreated, low blood sugar can damage baby’s brain and lead to developmental concerns.
  • Other neonatal complications – Babies of mothers with GDM are at an increased risk of respiratory distress, jaundice, and some more rare complications.
  • Long term risks – GDM increases risk of childhood obesity and Type 2 Diabetes.

Who is most at risk of gestational diabetes?

It’s important to know that GDM is not caused by anything you have done or haven’t done. It develops due to a complex interplay of risk factors, including changes in hormones during pregnancy that affect how your body processes glucose.

Gestational Diabetes can affect women of any age, shape, size, fitness level, education, or background — including those who are following a healthy diet and lifestyle.

However, some women have a higher risk of developing Gestational Diabetes. Risk factors for GDM include:

History of GDM in a previous pregnancy, previous issues with elevated blood sugar levels, age >40 years, high BMI, family history of Type 2 Diabetes or GDM, previous large baby, Middle Eastern, Indian, Asian, Aboriginal, Melanesian, Polynesian descent, PCOS, rapid weight gain during the first half of pregnancy or those on some medications eg steroids, antipsychotics.

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