Fixed mortgage rates remained virtually unchanged in the week ending May 14, but hybrid adjustable-rates inched lower, according to Freddie Mac's (FRE) Primary Mortgage Market Survey released today. Thirty-year fixed-rate mortgages averaged 4.86% with an average 0.6 point, up slightly from last week's 4.84% average. The 15-year Fixed-rate mortgage rose from an average 4.51% to 4.52% this week. “Interest rates for fixed-rate mortgages were little changed this week following the release of April’s employment figures,” said Frank Nothaft, Freddie Mac vice president and chief economist.  “The economy lost 539,000 jobs, less than the monthly job loss of the past five months, and the unemployment rate rose to 8.9%. ARM rates, however, fell slightly over the period." Five-year Treasury-indexed ARMs averaged 4.82% this week, down from last week's 4.90% average and well below 5.57%, the average recorded last year at this time. One-year Treasury-indexed ARMs dropped as well, from 4.78% to 4.71%. A separate rates survey conducted by Bankrate.com revealed findings similar to those of Freddie Mac. The benchmark 30-year, fixed-rate mortgage fell 6 basis points to 5.21%, according to Bankrate, while the Five-year ARM fell a much more significant 26 basis points to 4.81%. Nothaft says relatively low house prices and interest rates continue to help first-time home buyers.  "Housing affordability for the median first-time buyer reached an all-time record high in the first quarter since the NAR index began in 1981," he says. "Consequently, first-time home buyers accounted for half of existing home sales in the first three months of this year." And now, after an announcement Tuesday by the US Department of Housing and Urban Development, buyers will be allowed to use their first-time home buyer tax credits as down payments on FHA-insured loans. Write to Kelly Curran.