I always thought this was a pretty straightforward issue from a rationalist perspective—we have the technology to figure out whether the foetus has an active brain and can meaningfully perceive pain.
I see no reason to believe that you can in general kill a person because the person can’t perceive pain. Congenital insensitivity to pain is a thing.
I see no reason to believe that you can in general kill a person because the person can’t perceive pain. Congenital insensitivity to pain is a thing.
“Active brain” is also a term that wide open.