Reference Values During Pregnancy

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1 hour Oral Glucose Tolerance Test, OGTT, GTT , one hour oral glucose challenge test, GCT (serum, plasma)

   Units Fasting 1 hour    
mg/dL Not required 130 or  140     
mmol/L Not required 7.2 or 7.8    

The one hour oral glucose challenge test [GCT] is a screening test for gestational diabetes that measures plasma or serum glucose concentration 1 hour after a 50-g oral glucose load.  A blood sugar value >140 mg/dl (7.8 mmol/l) identifies approximately 80% of women with gestational diabetes (GDM),  a cutoff of >130 mg/dl (7.2 mmol/l) identifies 90% of women with GDM.

The California Diabetes and Pregnancy Program recommends that women with values 140 mg/dl to 179 mg/dl should have  a 3-hour 100 gram oral glucose tolerance test (OGTT) within one week.  If the patient has a screening value > 180 mg/dl, a fasting blood sugar should be checked as soon as possible. If the fasting is > 95 and the one hour screening test > 180 mg/dl this provides two abnormal values and the 3 hour OGTT is not required.  If the fasting value is less than 95 then proceed with the 3 hour OGTT.

A glucose challenge test is not necessary in patients with a fasting plasma glucose level >126 mg/dl (7.0 mmol/l) or a casual plasma glucose >200 mg/dl (11.1 mmol/l) since these values meet the threshold for the diagnosis of diabetes.


1.  Guidelines for Care, California Diabetes and Pregnancy Program,2002
2. American Diabetes Association.Diagnosis and classification of diabetes mellitus. Diabetes Care. 2009 Jan;32 Suppl 1:S62-7. PMID:19118289

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