Is ac1 glycohemoglobin the best test for gestational diabetes?

No.: Gestational diabetes testing involves a screeing test with 50 grams of glucose in liquid, then checking the blood sugar level an hour later. If that level is too high, then a formal glucose tolerance test should be done (several hours long). An A1c level of glycohemoglobin which is elevated would be suspicious for gestational diabetes, but it's not the preferred diagnostic test.