The 1-hour glucose screening test, also known as the Glucose Challenge Test (GCT), is a routine procedure used in prenatal care to identify potential gestational diabetes. This condition involves elevated blood sugar levels that develop during pregnancy. The purpose of this initial screening is to measure how effectively a pregnant person’s body processes a standardized amount of sugar. This simple, initial step helps healthcare providers determine if a more comprehensive diagnostic test is necessary.
The Recommended Timeframe for Screening
The standard window for scheduling the 1-hour glucose test is between the 24th and 28th weeks of gestation. This timing is chosen because hormonal changes causing insulin resistance typically peak during the later half of the second trimester. The placenta produces hormones that interfere with the body’s ability to use insulin correctly, leading to higher blood glucose levels. Testing during this period provides the most accurate snapshot of risk when resistance is most likely present.
For some patients, testing may be recommended earlier in the pregnancy. Individuals with significant risk factors, such as a history of gestational diabetes or a high body mass index, may be screened in the first trimester. If early screening results are normal, the patient still typically undergoes the standard 24-to-28-week test. Screening ensures that any onset of gestational diabetes is detected and managed promptly.
How to Prepare and What to Expect During the Test
Preparing for the 1-hour screening test is simple, as fasting is usually not required. Healthcare providers recommend eating a regular, balanced meal beforehand. However, it is advised to avoid consuming excessive amounts of concentrated sugar, such as candy, juice, or soda, immediately prior to the appointment. Eating a balanced diet in the days leading up to the test supports accurate results.
The procedure begins with the patient quickly drinking a specific glucose beverage, which contains 50 grams of sugar. This solution, often flavored and similar to a sweet soda, must be consumed within a brief five-minute period. Timing begins immediately after the last sip of the drink.
The patient must wait exactly 60 minutes before the blood sample is collected. During this hour, patients must remain relatively inactive and refrain from eating, drinking anything other than water, or smoking, as these actions could alter the blood sugar level. Once the 60-minute mark is reached, a phlebotomist performs a single blood draw from a vein, and the test is complete.
Decoding Your Screening Results
The collected blood sample measures the blood glucose concentration one hour after the sugar load. The numerical result indicates how well the body used insulin to clear the sugar from the bloodstream. A result that falls below a predetermined cut-off point is considered a normal screening.
The specific threshold used to define a normal result can vary between healthcare providers and laboratories, but it is most commonly set at 140 milligrams per deciliter (mg/dL). Some clinics may utilize a lower cut-off of 130 mg/dL or 135 mg/dL. If the glucose level is less than the established threshold, the body is managing the sugar load appropriately, and no further testing is needed.
A result equal to or higher than the cut-off is considered an elevated or abnormal screening result. An elevated result does not automatically diagnose gestational diabetes. Instead, it signals the need for a follow-up diagnostic test to confirm or rule out the condition.
Next Steps Following an Elevated Result
When the 1-hour screening result is elevated, the next step is scheduling the 3-hour Oral Glucose Tolerance Test (OGTT). This secondary test is significantly more comprehensive and is required to definitively diagnose gestational diabetes. The 3-hour OGTT requires the patient to fast for at least eight hours before the test begins to establish a baseline blood sugar level.
The procedure involves an initial fasting blood draw, followed by consuming a more concentrated glucose solution, typically containing 100 grams of sugar. Unlike the screening test, the 3-hour test requires three additional blood draws taken at the 1-hour, 2-hour, and 3-hour marks after finishing the drink. The presence of two or more elevated blood glucose readings across the four samples confirms a diagnosis.
If a diagnosis is confirmed, the healthcare team develops a plan. This usually involves dietary changes, increased physical activity, and regular blood sugar monitoring. Early diagnosis and management reduce the risks of complications for both the patient and the baby throughout the remainder of the pregnancy.