Both Fannie Mae and Freddie Mac retained their hefty shares of mortgage-backed securities with something of a bump during the third quarter of 2011, according to a new Inside The GSEs analysis.The GSEs issued a combined $174.8 billion in MBS in the third quarter, a 12.8 percent increase from the second quarter. Compared to the third quarter of 2010, Fannie and Freddie saw an 11.2 percent decrease in MBS issuance during the first nine months of the year.