I have some issues with arbitrary choosing of segments of books, if you are then going to try to consider someone a member of a strong grouping anyway (you can pick and choose all you like, I even encourage it as it is at least some thought gone into it, but you are then following some remixed version at best). Still the old vs new testament stuff is well established (at least until it is not for some other debate, sticking with modern moral debates it is usually about the time homosexuality comes into play) so I can roll with that.
On the conception thing I am curious, I have not seen or heard the passages to that effect (and such a thing would have been quite useful at points, and I imagine made well known). I also have to wonder if it would be that useful as concepts of how pregnancy worked were not well developed however many thousands of years ago the books in question were cooked up. Delving deep into my memory of schoolboy RS I believe the counter argument to be provided for the exam board was something like "in Sermon on the mount young Mr Jesus emphasised the dignity of human life, if a life would then lack dignity, and an unwanted pregnancy can certainly lead to that, then why not?"
Likewise there are measures/yardsticks by which things are determined and allowed, with it skewing towards "only if a danger to the mother is posed" for the later ones. This can vary by region and all sorts of policy but it is considered from such angles.
It is at this point I usually note a wishy washy line in the sand and start probing for things to change it (contraception, morning after, chemical where foetus is reabsorbed.....) but I will not commit too hard to anything there.
I don't like choosing arbitrarily, either. However, I do believe the examples I'm giving are consistent with what Scripture states as regarding the New Testament church.
As to the dignity of human life, that's not something that you solve with what would Biblically be murder. Evil begets evil. That is a call for the community at large, the brethren, to step up their game. Jewish culture at the time was pretty bad about that, going so far as to posit that those born with malformities or generally ill circumstances were somehow sinning against God (or their parents). Books like Job, though, directly refute this idea, as does Jesus in his response to the disciples about the blind man in John 9:1-5. It's our job, as individuals, to help those in need. (I'm not sure what you do with someone that was, for example, brain-dead. There are definitely cases that aren't easy to handle, but they're also exceedingly rare in abortion statistics, and that's probably where someone from a Christian perspective would pray as to the right choice to make. In that case, the child is probably "dead" by any reasonable measure, and I would leave the decision up to the parents.)
As for the verse about conception, Jeremiah 1:5 and Psalms 139:13-16 speak to that. Whether they actually understood it or not, however, is immaterial, since for the purposes of this particular side discussion, we are assuming the Bible is true, and that it is the inerrant Word of God. So we have to, under those constraints, take it at face value, and assume that the willful destruction of a fetus is murder.
Again, I know there are non-Christians here, and do not believe that the Bible is the divinely-inspired Word of God, but in the context of it being true, I think it's a reasonable conclusion to make about Jesus' teachings.
EDIT: Please note, there's always a chance that I'm wrong. I'm absolutely sure that there are things in the Bible that I misinterpret just from simple failings of human knowledge and logic. I feel this one to be pretty straightforward, and it's certainly not an insignificant viewpoint within Christianity, but I'm sure you can find professing Christians that believe otherwise, and I'm certainly not trying to come across as the ultimate authority on all things Christian. All I can do is present what I and minds much greater than mine have been able to understand in Scripture.
My biggest issue personally is deciding when does that option come off the table. At which point do we classify the fetus as a person. It's not an answer I expect to find in the thread, or come to anytime soon, it's a question I've been thinking about for a very long time.
That's pretty much my feeling on the matter. For good or for ill, I'd like some clarity, some definition from a medical perspective, on what we consider to be "life".