Fannie Mae and Freddie Mac continued to shrink their retained investment portfolios in the first quarter of this year by focusing on paring their MBS holdings. The two government-sponsored enterprises held a combined $560.04 billion in their retained mortgage portfolios at the end of March. That was down 1.9 percent from the previous period and 16.7 percent below year-ago levels. At their current pace, Fannie and Freddie are...[Includes one data table]