There are two types of tests used to diagnose gestational diabetes.

1. Glucose Challenge Test (GCT) – a blood test is performed one hour after consuming a glucose drink. If the result is considered high, you will be requested to have an oral glucose tolerance test.
2. Oral Glucose Tolerance Test (OGTT) – this test is performed after fasting overnight. A blood sample is collected before, and at one and two hours after consuming glucose drink.

Some women will be tested earlier than 28 weeks if they have had gestational diabetes previously or are considered to be at a higher risk for developing gestational diabetes.

Why test at around 28 weeks gestation?

Gestational diabetes most commonly develops around the 24th - 28th week of pregnancy. Around this time your hormone levels are higher than they were earlier in pregnancy and there is a progressive need for the body to produce more insulin. When the body cannot compensate by increasing insulin secretion, gestational diabetes occurs. The increase in insulin secretion is greatest in the third trimester. Diagnosis at this stage allows time to manage and control the baby's growth.

What do the results mean?

Gestational diabetes is diagnosed if any one of the glucose levels are equal to or above:

• 5.5 mmol/L fasting (before having the drink)
• 8 mmol/L after 2 hours

These figures are based on current guidelines from the Australasian Diabetes in Pregnancy Society (ADIPS).

Gestational diabetes does not usually give rise to symptoms so it is very important to be tested in your pregnancy.