Oral Glucose Tolerance Test in Pregnant Woman

 

Test Preparation:

(1) Starting 3 days prior to test, the patient receives a diet containing 150 g of carbohydrate per day.

(2) The patient must not be stressed by illness prior to or during the test.

(3) All nonessential medications should be discontinued at least 3 days prior to testing; many medications can impair glucose tolerance.

(4) A 10-16 hour fast is recommended.

(5) Undue exercise before or during the test is to be avoided.

(6) No coffee or smoking is allowed once the fast has started or during the test.

 

Dose of glucose for test:

(1) screening test: 50 grams orally

(2) diagnostic test: 100 grams orally

 

Oral glucose solutions come in 10 US fluid ounces (296 mL) bottles containing 50, 75 or 100 grams of glucose (5, 7.5 and 10 g per fluid ounce).

 

50 gram oral screening test:

The serum glucose is measured 1 hour after the dose and if it exceeds the cutoff then the 100 gram diagnostic test is performed:

(1) The cutoff prior to 1997 was >= 150 mg/dL.

(2) The current cutoff is >= 130 mg/dL

 

100 gram oral diagnostic test:

The diagnosis of gestational diabetes requires that at least 2 glucose values exceed the cutoffs for various times.

 

Cutoffs for the 100 g oral test from the National Diabetes Data Group (NDDG)

Specimen	Serum	Whole Blood
fasting	105 mg/dL	95 mg/dL
1 hour	190 mg/dL	170 mg/dL
2 hour	165 mg/dL	149 mg/dL
3 hour	145 mg/dL	130 mg/dL

 

Current cutoffs for the 100 g oral test (after Carpenter and Coustan)

 

Specimen	Serum	Whole Blood
fasting	95 mg/dL	86 mg/dL
1 hour	180 mg/dL	162 mg/dL
2 hour	155 mg/dL	140 mg/dL
3 hour	140 mg/dL	126 mg/dL

 

where:

• Glucose in whole blood is 90% of that in serum or plasma.