Two reasons I'm against this move. 
My 1st born was 25 weeks term, weighing ~600gm. We were cautioned to expect still birth; he lived just 26hrs in an ICU.  This is not a viable stage for a fetus. 
My 2nd wife had stopped menstruating when her doctor prescribed drugs for some condition.  (I'm not clear on the details as we were not married at the time.). When he found out she was pregnant instead of menopausal, he recommended an abortion. Years later she still struggled with that decision, even though it was correct for all concerned, including her existing family.

I'm not in favor of using abortion as birth control. But neither am I in favor of taking this medical option away from doctors and families.