Two-step screening:
Administer a nonfasting 50-g oral glucose challenge test.
If the value meets or exceeds the thresholds below and is ≤ 200 mg per dL (11.1 mmol per L), administer a 100-g oral glucose tolerance test.
Diagnose GDM if two or more values on a 100-g test meet or exceed the thresholds below.
The American Diabetes Association does not consider a value > 200 mg per dL on a 50-g oral glucose challenge test to be necessarily diagnostic of GDM; however, it is reasonable to treat these patients empirically as if they have GDM (without performing a 100-g oral glucose tolerance test) because they require insulin during pregnancy more often than patients with GDM diagnosed using the 100-g test.
Test	Time	Threshold for abnormal result		Comments
50-g oral glucose challenge test	1 hour	130 mg per dL (7.2 mmol per L)		Use of any threshold value is acceptable.
			or	A cutoff of 130 mg per dL is more sensitive (99% vs. 85%) but less specific (77% vs. 86%) compared with a cutoff of 140 mg per dL.
		135 mg per dL (7.5 mmol per L)
			or
		140 mg per dL (7.8 mmol per L)
		Threshold for abnormal result
Test	Time	Carpenter and Coustan criteria15		National Diabetes Data Group criteria16	Comments
100-g oral glucose tolerance test	Fasting	95 mg per dL (5.3 mmol per L)		105 mg per dL (5.8 mmol per L)	Use of either set of criteria is acceptable.
	1 hour	180 mg per dL (10.0 mmol per L)		190 mg per dL (10.5 mmol per L)
	2 hours	155 mg per dL (8.6 mmol per L)		165 mg per dL (9.2 mmol per L)
	3 hours	140 mg per dL (7.8 mmol per L)		145 mg per dL (8.1 mmol per L)
One-step screening:
Administer a fasting 75-g oral glucose tolerance test.
Diagnose GDM if one or more thresholds are met or exceeded.
Test	Time	Threshold for abnormal result		Comments
75-g oral glucose tolerance test	Fasting	92 mg per dL (5.1 mmol per L)		Compared with the two-step approach, the one-step approach results in a higher prevalence of GDM (6% vs. 15% to 20%).
	1 hour	180 mg per dL (10.0 mmol per L)
	2 hours	153 mg per dL (8.5 mmol per L)