Americans Choose Life?

I just came across an interesting article, here's a snippet:

NEW YORK - The Gallup Poll reported Friday that 51 percent of Americans now call themselves "pro-life" rather than "pro-choice" on the issue of abortion, the first time a majority gave that answer in the 15 years that Gallup has asked the question.

The findings, obtained in an annual survey on values and beliefs conducted May 7-10, marked a significant shift from a year ago. A year ago, 50 percent said they were pro-choice and 44 percent pro-life — in the new poll, 42 percent said they were pro-choice.

I must admit, this really surprises me. I wonder what accounts for the shift?