How did "pro-choice" and "pro-life" become the names of the two major sides in the abortion debate?

by EUPW

I'm asking about the names themselves.

Edit: I probably should have said, "the two major sides in the United States."

DigChrono

Slightly related: were there names different from the current ones for the pro/anti abortion movements in the past?

william_sr

It seems pretty straightforward. What is the ultimate value for one group and what is the ultimate value for the other?

"A woman's right to choose."

"Defend life from conception to natural death."