Glucose Challenge Test During Pregnancy
Diabetes
Obie Editorial Team
The 1-hour glucose challenge test or GCT, measures the effect of a glucose solution on blood glucose levels. The GCT does not necessarily diagnose diabetes but it screens women who may be at risk and who may need a 3-hour glucose tolerance test or GTT. A blood sample is taken 1-hour after ingesting a glucose solution. The glucose solution, which is typically flavored, contains 50 - 100 grams of glucose (sugar).
ACOG supports the "2-step" approach to diagnosing diabetes in pregnancy
Note: Diagnosis of GDM is based on 2 abnormal values on the 3-hour OGTT
ACOG recommends that currently there is insufficient evidence to diagnose GDM based on only one abnormal value
Patients with only one elevated value may require additional surveillance
Typically, the 1-hour glucose tolerance test is given first with the 3-hour glucose tolerance test reserved for women who fail the initial test.
This screening test is done to identify who may be at risk of diabetes and normally given in the 28th week of pregnancy. It does not usually diagnose diabetes but is performed to identify those who require additional testing for gestational diabetes.
If the test results are below 130 mg/dl (or below 135/140 mg/dl) then no additional testing is required. If the test is above 130 mg (135 or 140 mg) then a 3-hour glucose tolerance test or GTT is ordered. The 3-hour glucose tolerance test uses a 100-gram glucose solution.
If non-fasting glucose levels are greater than 126 mg/dL or normal daily glucose levels are greater than 200 mg/dL, glucose tolerance testing is not necessary as these measurements indicate diabetes.
A glucose threshold value >140 mg/dL identifies approximately 80% of women with pregnancy diabetes (GDM), and the yield is further increased to 90% by using a cutoff of >130 mg/dL. Women whose serum glucose is above the threshold value on the GCT (130-140 mg/dL) have a diagnostic 3-hour GTT done to find out if they have diabetes.
The 3-hour GTT consists of drinking 100g of glucose and having four blood samples drawn: fasting, and then 1, 2, and 3 hours after the drink. Cutoff values for the 3-hour GTT are as follows:
Pregnant women with two or more elevated values are considered to have gestational diabetes mellitus (GDM), though even one elevated value increases certain risks.
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Gestational diabetes carries the same symptoms and problems as other forms of diabetes not associated with pregnancy because the body loses the ability to handle food sugars and insulin development.
The glucose challenge test does not necessarily diagnose diabetes but it screens women who may be at risk and who may need a 3-hour glucose tolerance test or GTT.
Type 1 diabetes, commonly referred to as juvenile diabetes, is typically diagnosed in children or young adults, though diagnosis can occur in any stage of life. Of the nearly 26 million people in the United States with diabetes, only 5% have type 1 diabetes.