Must the State allege the prior convictions in the charging document and prove them at trial beyond a reasonable doubt?

No. The State is not statutorily or constitutionally required to allege prior convictions in this context. The prior convictions are not elements of the offense; nor do they elevate a Class 3 misdemeanor to an offense of a higher class. Rather, they place the defendant in a higher prior conviction level for a Class 3 misdemeanor. (For convictions that elevate an offense to a different class and are thus an element of the higher offense, such as a fourth worthless check offense under G.S. 14-107(d)(1), the State must allege the priors in the charging document. G.S. 15A-924(a)(5); G.S. 15A-928.)