Gestational Diabetes Mellitus (GDM) is a specific type of diabetes that occurs due to pregnancy. It affects about 15% of pregnancies. It occurs due to increased insulin resistance because of hormones produced by the placenta. Insulin normally moves sugar out of the blood stream into the cells of the body, reducing blood sugar levels. When GDM occurs the body cannot produce enough insulin to achieve this and blood sugar levels may run high. Identifying and treating Gestational Diabetes reduces risks to you and your baby.
Most women undergo testing for Gestational Diabetes at 26 to 28 weeks. In certain high risk groups testing will occur earlier in the pregnancy after 10 weeks.
The test is called the oral glucose tolerance test (GTT) which is a fasting test. This normally needs to be booked with pathology providers:
- Fasting is required for a period of 8-10 hours prior to the test. (No food or fluids such as tea, coffee or fruit juice.)
- You may drink water at any time prior to and during the test.
- Testing is generally conducted in the morning.
During the test:
- First a fasting blood sample is collected.
- You will then be given a 75g bottle of glucose to drink within 5 minutes.
- A 1 hour post glucose blood sample collected.
- A 2 hour post glucose blood sample collected.
- You will be at the collection centre for around two and a half hours.
Current evidence suggests that there is a benefit of reduced perinatal morbidity, with the use of screening programs for GDM, and treating women who are diagnosed with it. For over 20 years, the diagnosis of GDM has been derived from an ad hoc consensus, based on very limited data available at that time.1 When screening for GDM, there should be uniformity in the testing used and the subsequent follow-up management. The landmark observation trial HAPO, 20082 and other important randomised trials (Crowther et al. 20053 Langdon et al. 20094) have led to recommendations for new criteria for the diagnosis of GDM2, which have been endorsed by the World Health Organisation (WHO)5.
The following is recommended:
Biochemical screening for Gestational Diabetes should be performed at 26-28 weeks of gestation. Earlier testing performed in women at particularly high risk should be repeated at 24-28 weeks gestation to test for GDM, if a negative result is obtained at the earlier testing time point.
RANZCOG recommended screening regimen is a 75gram two-hour Pregnancy Oral Glucose Tolerance Test (POGTT). A two-step procedure involving an initial one-hour non-fasting oral Glucose Challenge Test (GCT) is no longer recommended.
The full set of criteria can be viewed at the following link
