Heavy refinance volume pushed both Fannie Mae and Freddie Mac single-family mortgage securitization up sharply during the third quarter of 2012, well ahead of the pace the two GSEs set in 2011, according to a new Inside The GSEs analysis. Fannie and Freddie issued $335.38 billion in single-family mortgage-backed securities during the third quarter, a 22.4 percent increase from the second quarter, a rebound from the GSEs’ slump during the April-through-June period.