CHICAGO — A large majority of residents and fellows at Northwestern Medicine hospitals and clinics voted in favor of unionizing, making them the biggest union of medical house staff in the Midwest with nearly 1,300 doctors. The National Labor Relations Board’s Chicago office started the ballot count Monday morning and found the McGaw Medical Center of Northwestern University workers voted 794 to 148 in favor of union representation, Kayla Blado, board spokesperson, said in a statement. The results will be certified by the board in the coming week. The residents, chief residents, fellows and in…