I see that some of us get cranky when outquipped, and that some of us aren't very good at comparasions--note to Kane: "painfully obvious," and, "probably," are probably best avoided in arguments, because they make it painfully obvious that you're probably reaching too far for a comparasion you can't sustain.
I also see that--surprise, surprise, surprise--much of this boils to men telling women what to do with their bodies, and arguing with each other over the details.
Incidentally--not that reality will bother--historically speaking, the fetus was apparently not considered viable until it began to, "quicken," to kick, that is, in a way that could be felt, somewhere around 6-7 months gestational age.
Most of the fussbudgeting is modern, and appeared--surprise, surprise!--about the time that a) capitalism needed more bodies, b) decent contraception began to be available, c) women began to be, 'a problem.'
This isn't about a fetus; it's about the Preservation of the Almighty Sperm. This isn't about trimesters; it's about men's control of women. So let's ask the REAL question--why don't you trust women to think the matter through, and make the right decision for themselves?