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Table 2.5

Screening for and diagnosis of GDM

One-step strategy 
Perform a 75-g OGTT, with plasma glucose measurement when patient is fasting and at 1 and 2 h, at 24–28 weeks of gestation in women not previously diagnosed with overt diabetes. 
The OGTT should be performed in the morning after an overnight fast of at least 8 h. 
The diagnosis of GDM is made when any of the following plasma glucose values are met or exceeded: 
 • Fasting: 92 mg/dL (5.1 mmol/L) 
 • 1 h: 180 mg/dL (10.0 mmol/L) 
 • 2 h: 153 mg/dL (8.5 mmol/L) 
Two-step strategy 
Step 1: Perform a 50-g GLT (nonfasting), with plasma glucose measurement at 1 h, at 24–28 weeks of gestation in women not previously diagnosed with overt diabetes. 
If the plasma glucose level measured 1 h after the load is ≥140 mg/dL* (7.8 mmol/L), proceed to a 100-g OGTT. 
Step 2: The 100-g OGTT should be performed when the patient is fasting. 
The diagnosis of GDM is made if at least two of the following four plasma glucose levels (measured fasting and 1 h, 2 h, 3 h after the OGTT) are met or exceeded: 
 Carpenter/Coustan (56) or NDDG (57) 
• Fasting 95 mg/dL (5.3 mmol/L)  105 mg/dL (5.8 mmol/L) 
• 1 h 180 mg/dL (10.0 mmol/L)  190 mg/dL (10.6 mmol/L) 
• 2 h 155 mg/dL (8.6 mmol/L)  165 mg/dL (9.2 mmol/L) 
• 3 h 140 mg/dL (7.8 mmol/L)  145 mg/dL (8.0 mmol/L) 
One-step strategy 
Perform a 75-g OGTT, with plasma glucose measurement when patient is fasting and at 1 and 2 h, at 24–28 weeks of gestation in women not previously diagnosed with overt diabetes. 
The OGTT should be performed in the morning after an overnight fast of at least 8 h. 
The diagnosis of GDM is made when any of the following plasma glucose values are met or exceeded: 
 • Fasting: 92 mg/dL (5.1 mmol/L) 
 • 1 h: 180 mg/dL (10.0 mmol/L) 
 • 2 h: 153 mg/dL (8.5 mmol/L) 
Two-step strategy 
Step 1: Perform a 50-g GLT (nonfasting), with plasma glucose measurement at 1 h, at 24–28 weeks of gestation in women not previously diagnosed with overt diabetes. 
If the plasma glucose level measured 1 h after the load is ≥140 mg/dL* (7.8 mmol/L), proceed to a 100-g OGTT. 
Step 2: The 100-g OGTT should be performed when the patient is fasting. 
The diagnosis of GDM is made if at least two of the following four plasma glucose levels (measured fasting and 1 h, 2 h, 3 h after the OGTT) are met or exceeded: 
 Carpenter/Coustan (56) or NDDG (57) 
• Fasting 95 mg/dL (5.3 mmol/L)  105 mg/dL (5.8 mmol/L) 
• 1 h 180 mg/dL (10.0 mmol/L)  190 mg/dL (10.6 mmol/L) 
• 2 h 155 mg/dL (8.6 mmol/L)  165 mg/dL (9.2 mmol/L) 
• 3 h 140 mg/dL (7.8 mmol/L)  145 mg/dL (8.0 mmol/L) 

NDDG, National Diabetes Data Group.

*The ACOG recommends a lower threshold of 135 mg/dL (7.5 mmol/L) in high-risk ethnic populations with higher prevalence of GDM; some experts also recommend 130 mg/dL (7.2 mmol/L).

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