10th week A1c could predict GD

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Women who went on to develop gestational diabetes had higher HbA1c levels (an average of 5.3 percent), compared to those without gestational diabetes (an average HbA1c level of 5.1 percent). Each .1 percent increase in HbA1c above 5.1 percent in early pregnancy was associated with a 22-percent higher risk for gestational diabetes.

Come to think of it, that's not a very large difference and what about the margin for errors. But, a study is a study.

https://www.nichd.nih.gov/news/releases/081618-gestational-diabetes