Diagnostic Options for GDM
The thought of developing Gestational Diabetes Mellitus [GDM] once falling pregnant for some women feels unlikely. Many women who eat a healthy diet and get regular exercise often will not consider checking if they have GDM, as it is misleadingly thought to be caused by poor eating habits and a sedentary lifestyle.
The hormones the placenta and body release during pregnancy, such as progesterone, are designed to create insulin resistance in our
bodies. This can affect the how the main source of energy - glucose, travels to the baby to help it grow. For more information on the causes of GDM, check out our What is Gestational Diabetes page.
Universal screening for GDM is recommended for all women in Australia. Among first time mothers, or women being first diagnosed with GDM, their options for testing are often not discussed.
The diagnostic process plays a crucial role in identifying this condition early on, allowing for timely intervention and support. To determine if you have GDM you have three options for testing which include:
Which Option is Right for me?
2 hour ogtt
The oral glucose test (OGTT) is a common and widely accepted method for diagnosing gestational diabetes. It is usually the first test recommended by clinicians for diagnosing GDM. The OGTT involves drinking a concentrated glucose solution, followed by blood tests to measure how efficiently the body processes sugar.
The OGTT requires fasting overnight (drinking water is fine) with a test at a pathology centre first thing in the morning (make sure your book ahead). A blood sample is taken to understand the fasting glucose level, followed by drinking a concentrated glucose solution. A further 2 blood samples will be taken over the next 2 hours to check your bodies response to a high glucose intake. Make sure your phone is charged or you have a book, as you need to stay at the pathology centre until the test is completed.
The pros of this approach are that this is an accurate way of diagnosing GDM through monitoring your bodies response to a glucose load and this procedure can be undertaken most pathology centres.
However, some expectant mothers may find consuming the glucose solution unpleasant and the process itself time consuming.
Fasting Glucose Testing
A blood test of the fasting glucose level is the quickest and least invasive test for diagnosing GDM.
This test involves fasting overnight (drinking water is fine) with a blood sample collect at a pathology centre first thing in the morning. A fasting glucose test can be ordered by a midwife, GP or obstetrician. While this method provides a snapshot of blood glucose levels,
it will not capture the nuances of glucose fluctuations throughout the day.
Your clinician may also order a test of HbA1c as part of this fasting glucose test. HbA1c testing looks at the levels of glucose bound to
red-blood cells. Red-blood cells live for approximately 120 days, so this can provide a snapshot of your average glucose levels over a 4-month period.
However, as pregnancy progress into the third trimester, the red-blood cell life span reduces. This means that a HbA1c test alone is a less reliable test later in pregnancy. Additionally, this test is not always recommended for people who have a condition which may affect the production of normal red-blood cells, such as sickle-cell anaemia.
The use of the Fasting Glucose test was popular at the height of Covid, as it only requires a single blood sample. At the time this was a preferred option over the 2hr OGTT test, as this test required the pregnant women to sit in the testing centre for two hours with potentially unwell patients surrounding them.
Research suggests that relying solely on fasting glucose levels and HbA1c may miss a significant percentage of women with gestational diabetes. During Covid it was thought that by not having the 1-hour and 2-hour blood glucose results from the 2hr OGTT, around 20% of women were mis-diagnosed.
Self-Blood Glucose Monitoring
For a more comprehensive understanding of blood glucose dynamics, some healthcare providers recommend at home blood glucose monitoring over a two-week period with a glucometer. This method may also be recommended for women whom have had gastric surgery as the way food and nutrients are metabolised in these women can vary.
This approach offers a real-time, detailed view of how blood glucose levels respond to various factors like diet, exercise, and pregnancy hormones. Women who are diagnosed with GDM will also be recommended to continue monitoring their blood glucose levels with a glucometer throughout the remainder of their pregnancy.
However, this method is a little more invasive and not all women may feel comfortable with taking a glucose ready by pricking their fingers four times a day. In some cases, it will also be required to log daily exercise and food intake to an app to assist in a diagnosis. There may be a cost outlay in terms of purchasing testing equipment such as a glucometer, lancet drums and testing strips.
Understanding the longer-term blood-glucose levels provides some advantages, but will also take longer for a clinician to return a diagnosis over a 2hr OGTT or Fasting Glucose blood test.
Summary
Each testing method comes with its own set of pros and cons, and the choice often depends on individual factors such as lifestyle, preferences, and medical history. Striking a balance between accuracy and practicality is essential for ensuring expectant mums receive timely and appropriate care.
Ultimately, a collaborative discussion between the healthcare provider and the pregnant individual is important in selecting the most
suitable approach for gestational diabetes testing. Regular prenatal care and open communication can empower mums to navigate the complexities of GDM with confidence and ensure the best possible outcomes for both you and your baby.