New production of MBS backed by adjustable rate mortgages dropped 4.8 percent from the fourth quarter of 2005 to the first three months of this year, according to a new analysis and ranking by Inside MBS & ABS. A total of $237.8 billion of ARM loans were securitized in the first quarter, or about 47 percent of total MBS issuance during the period. Compared to a year ago, ARM securitization volume was actually up slightly. … [One data table included]