Gestational diabetes mellitus (GDM) is defined as any degree of glucose intolerance with onset or first recognition during pregnancy (Metzger BE, Coustan DR Diabetes Care 21 Suppl.2, B1-B167, 1998) . It is generally accepted that the diagnosis of gestational diabetes should be based on blood glucose testing.

Two different approaches may be selected for diagnosis:

The one-step approach: Consisting on the performance of an oral glucose tolerance test (OGTT) without previous blood glucose testing. This approach is recommended in high risk populations.

The two step approach: A first step measuring plasma or serum glucose 1 hour after a 50-gr. oral glucose load (glucose challenge test or GCT), and on those women with values exceeding the diagnostic threshold, a second step performing an oral glucose tolerance test (OGTT).

Regardless of the approach used, the diagnosis of GDM is based on the results of the oral glucose tolerance test.