The briefest look at the way the question was phrased lets those capable of analysis grok why the response to that question is contradicted by a subsequent one. It asked "are you pro-life"? Who is going to say "No" to that? A later question.. "do you believe in abortion in the first trimester"? scored 73% from the same people!
"Identifying oneself" as "pro-life" or "pro-choice" is NOT an ambigious, , "could be this, might mean that" type of thing. Americans know EXACTLY what is meant by those terms. Sorry.