Both Fannie Mae and Freddie Mac held onto their ample shares of mortgage-backed securities with something of a bump during the first quarter of 2012, according to a new Inside The GSEs analysis. The GSEs issued a combined $303.9 billion in MBS during the first quarter, a 13.9 percent increase from the fourth quarter of 2011. Compared to the first quarter of last year, Fannie and Freddie saw a 16.4 percent increase in MBS issuance. Between the two companies, Fannie and Freddie registered a plentiful 77.9 percent share of new MBS during the period that ended March 31, 2012, up from 77.1 percent the two companies held during the fourth quarter of 2011 and much farther apart from the 74.8 percent both GSEs held during the first quarter of 2011.