The 1-hour Glucose Tolerance Test is a routine screening often performed during pregnancy. It evaluates how effectively the body processes sugar, or glucose, its primary energy source. This test helps identify individuals who might have difficulty regulating their blood sugar levels.
What is the 1-Hour Glucose Tolerance Test?
The 1-hour Glucose Tolerance Test (GTT), also known as the glucose challenge test, is a common screening tool. Its main purpose is to screen for gestational diabetes, a type of diabetes that develops specifically during pregnancy. This screening is important because high blood sugar levels during pregnancy can affect both the pregnant individual and the developing fetus.
Undiagnosed or unmanaged gestational diabetes can lead to various complications, including an increased risk of preeclampsia and a larger-than-average baby, which may cause difficulties during birth. The test is typically performed between the 24th and 28th weeks of pregnancy. However, if risk factors are present, healthcare providers might recommend earlier screening.
Interpreting Your Test Results
After the 1-hour glucose tolerance test, your blood sugar level is measured one hour after consuming the glucose solution. For most laboratories and guidelines, a normal result is a blood sugar level equal to or less than 140 mg/dL (7.8 mmol/L), meaning no further immediate action is required for gestational diabetes screening. Some clinics may use a threshold of 130 mg/dL (7.2 mmol/L).
If your blood glucose level is above this range, it indicates the need for further testing but does not confirm a diagnosis of gestational diabetes. An elevated result simply suggests your body might not be processing sugar as efficiently as expected. For example, a blood sugar level between 140 mg/dL and 199 mg/dL usually prompts a follow-up diagnostic test, indicating a higher risk that requires additional evaluation.
Preparing for the Test and What to Expect
Preparing for the 1-hour glucose tolerance test is generally straightforward, as fasting is not typically required. You can usually eat and drink as you normally would, though some providers may suggest avoiding excessively sugary foods or drinks immediately beforehand. Inform your doctor about any medications you are taking, as some can affect blood glucose levels.
The test involves drinking a sweet liquid containing 50 grams of glucose within a few minutes. After drinking the solution, you will wait for one hour, during which you should not eat or drink anything except plain water. Following this waiting period, a blood sample will be drawn to measure your blood glucose level. Some individuals might experience mild side effects, such as nausea, lightheadedness, or sweating after drinking the sugary solution.
What Happens After an Abnormal Result?
If your 1-hour glucose tolerance test result is above the normal threshold, the next step typically involves a follow-up diagnostic test. This usually means undergoing a 3-hour glucose tolerance test. The 3-hour test is more rigorous and is designed to definitively diagnose or rule out gestational diabetes.
For the 3-hour test, you will need to fast for 8 to 14 hours beforehand, consuming only sips of water. A blood sample will be drawn to measure your fasting blood sugar level. After this initial blood draw, you will drink a more concentrated glucose solution, typically containing 100 grams of glucose. Additional blood samples will then be collected at one, two, and three hours after you finish the drink. You will need to remain at the clinic throughout this period, as activity can interfere with the accuracy of the results.