Glucose intolerance during pregnancy is associated with an increase in perinatal morbidity and mortality, especially in women who are:

• Aged >25 years
• Member of an ethnic group with high prevalence of diabetes (e.g., Hispanic, African, Native American, South or East Asian, Pacific islander)
• Body mass index > 25
• Previous unexplained perinatal loss or birth of a malformed child
• History of abnormal glucose tolerance
• Previous large baby (greater than 9 lbs.)
• Family history of diabetes, especially in first degree relatives
• Abnormal birth weight (<> 9 lbs)
• Polycystic ovary syndrome

Hyperglycemia during pregnancy affects 2-3% of pregnant women; most will return to normal after delivery. Most patients with GDM have normal fasting glucose levels, thus some challenge of glucose tolerance must be undertaken. It is therefore recommended that universal screening and diagnosis be performed between 24 and 28 weeks gestation on all pregnant women not identified as having glucose intolerance. Women with a family history of diabetes or previous gestational diabetes should undergo the screening test earlier in pregnancy (14 to 20 weeks) and again at 24 to 28 weeks of gestation.


1. Patient Preparation:
Explain test purpose (to evaluate abnormal carbohydrate metabolism) and the procedure. No fasting is required. Test performed without regard to time of day or time of last meal. Patient should not eat, drink, or chew gum during the test. She may void if necessary.

2. Have patient ingest 50 gm of oral glucose (usually chilled glucola).

3. One hour after ingestion, measure patient’s serum glucose.

4. Patient aftercare: Normal activities, eating, and drinking may be resumed.

5. Normal Values: <> 140 mg/dL (nonfasting) / > 130 mg/dL (fasting) and <> 126 mg/dL are diagnostic of diabetes.


1. Perform in the morning after a 10-16 hour fast.
Note: This is often done after a 3-day 150-gm carbohydrate/day diet.

2. Measure fasting serum glucose

3. Have patient ingest 100 gm of glucose orally within 5 minutes

4. Measure serum glucose hourly for 3 hours – Fasting, 1 hour, 2 hour, 3 hour

5. The patient should not smoke, drink coffee, or exercise during the testing process other than to walk around. If autonomic nervous system responses develop during testing (pallor, sweating, nausea, fainting, etc.), testing should be discontinued after a sample is taken. The test should be repeated at another time.

6. Normal venous glucose values:

Fasting <95 mg/dL
1 hour <180 mg/dL
2 hour <155 mg/dL
3 hour <140 mg/dL

7. If two or more of the four values are met or exceeded a diagnosis of gestational diabetes can be made.

8. If results are normal in a clinically suspicious situation, repeat during the third trimester.


1. Fischback, T, Dunning, MB III. Manual of Laboratory Diagnostic Tests, LW & W, Philadelphia, PA, 7th Ed, 2003.

2. Star, Winifred. Ambulatory Obstetrics, Univ. of California San Francisco; 3rd Ed, 1999.

3. Tietz NW. Textbook of clinical Chemistry, 3rd Ed. WB Saunders. Philadelphia: 1815; 1999.

4. Wallace, J. Interpretation of Laboratory Tests, LW & W, Philadelphia, PA, 7th ed. 2000.


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