Lending had actually loosened slightly in December, before the new rules went into effect.
"2013 closed with the loosest credit requirements of the year," said Jonathan Corr, president of Ellie Mae, a mortgage software and data company, in a report released Wednesday. "The average FICO score for all closed loans last month was 727, 11 points below the 2013 average and 21 points lower than December 2012."
Last month, 31 percent of closed loans had FICO scores below 700, compared with 21 percent in December 2012, according to the report.
(Read more: New mortgage rules may favor the wealthy)
Looking at a daily rate monitor from Mortgage News Daily, the average rate on the 30-year fixed began its slide Friday, after the release of the underwhelming December jobs report from the Labor Department. It fell from 4.62 percent Thursday to 4.52 percent by the end of the day Friday. By Monday, it was at 4.47 percent, but then came up again Tuesday to 4.50 percent.
—By CNBC's Diana Olick. Follow her on Twitter
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