Both Fannie Mae and Freddie Mac retained their dominant shares of mortgage-backed securities with something of a slide during the second quarter of 2012, according to an Inside The GSEs analysis. The two GSEs issued a combined $273.9 billion MBS during the second quarter, a 10.2 percent decrease from the first quarter. Compared to the second quarter of last year, however, Fannie and Freddie saw an ample 76.8 percent increase in MBS issuance.