I mean no offense with the following contents. Please. I've to rewrite this after spending 45 minutes writing it on my phone only to have the shitty browser at&t forces me to use derp out. A lot of baby seals will be clubbed, I can assure you.
I've thought long and hard on both sides, and I've come up with a logical standpoint on the whole 'murder' part of this using my knowledge of biology and mixed with logic and reason. They're pretty logical standpoints, and again, I mean no offense.
Pro-life:
From AL's posts, I've actually shocked myself with my analytical opinion. Here's how a pro-lifer's argument could make sense (I say could because most notable pro-lifers never use whatever brain they have). I was going to say cells are not sentient, but I realized; cells have a nucleus and endoplasmic reticulum, which act to create and send information throughout the cell. This is a blueprint for every cell, as a fetus grows through cell division. During this process, cells become designated as cells for the brain, blood, bone, muscle, skin, etc. When enough are formed, they start to actually form a human fetus [Side note 1]. This is where you can call abortion murder. This is where it can be argued that a fetus is sentient, and is 'alive.'
Pro-Choice:
At the point where the fetus is looking a lot more human, and is sentient [2], pro-choice can now argue legitimately against "abortion=murder." Even if it is sentient, the fetus is not aware of its existence. Its eyes are still shut [3], and even after birth, validating its self-awareness is extremely hard [4].
The mother is, however, living, and has (hopefully) been sentient for at least 19 years at this point. She is capable of deciding whether or not she wants to go through with having a child. The fetus, however, doesn't even know what is being thought by its host. It is too busy readying itself to become a living, eating, thinking, breathing human being.
So what it comes down to in this is what is sentient enough for you?
Side notes:
1: Technically, the fetus can be called sentient when the brain, or brain cells, decide to look to see if they have two X chromosomes or not.
2: Sentient in a way of it knows what it needs to do, but that is it. It isn't aware.
3: Newborns' eyes are shut most of the time for relatively one to two weeks after birth.
4: We don't have the technology to see if a fetus is self-aware and sentient and all as if it isn't in the womb. Simply asking a person won't work either; unless they have a memory disorder or something of the sort, they will not recall any event before the age of three, unless it was a traumatic event. Alternatively, it is ridiculous to ask a two-year-old if they remember anything before they entered the world.