Kind of a delicate linguistic line I walk, hmmm? Every answer to such questions depends on careful regard for the relativity of the circumstances.
In everyday interface with other people, I DO treat other lives as valuble and deserving of care and consideration, but this does not mean that I see some intrinsic value to 'life' itself in relation to the Universe as a whole. If we are, as we seem to be, a complex, temporary hiccup in the state of one small planet in one average galaxy in one tiny corner of an unimaginably huge cosmos....then what does it mean to ascribe 'special value' to our minimal impact on it all?
But from our biased viewpoint, we are quite important, and we (individually & collectively) **impart** value to individual lives according to subjective views of what is worthwhile. How else can we explain a history which includes Mother Teresa, Albert Schweitzer...and Ghengis Khan and Adolph Hitler?

Now..in order to 'judge' some individual case, it again depends on the relative importance of the circumstance and the ...again... subjective view of what is involved. If presented with a situation where you must choose to lose some lives in order save others...how do you proceed? They had to do that on the Titantic...are women & children 'intrinsically' more valuble than ...say...a doctor? *shrug* I hope I am never faced with such a choice.
   Climbers on Mt. Everest regularly have to decide whether to risk several lives trying to rescue someone who is injured or out of oxygen in a precarious situation.
   In the same way, doctors have to decide when to try to save a baby at risk of the mother's life....or vice-versa. Often, their best advice runs counter to the wishes of the family.

So...what criteria do I use? What can I say? **IT DEPENDS!!** 20 years ago, my wife & I had to face that....we were trying to have another child, when amniocentesis revealed a condition in which the baby seldom survives to birth...and we were at 20 weeks! Even our doctor was opposed to abortion, but he offered no hope of successful outcome. You think we didn't agonize over what to do? I'll tell you this much...we did NOT apply some pre-digested standard worked out by some group claiming absolute knowlege of what was 'right'. And I'd never dream to tell someone else how to decide something like that, even if it was different from my own opinion.

In essence, that's what I mean by case-by-case....there are no absolute rules. There are sometimes laws which attempt to codify general attitudes, but some seem, as in Roe V Wade, to treat it like a game in which "if we get more votes, we can override their position, because WE have right on our side!"
The whole point of Roe V Wade was to allow those most affected, like my wife & I, to decide our own situation as best we could and NOT make it a rubber-stamp ruling based on some vague notion that it followed a subjective interpretation of some arcane religious text.

....well, you asked. I'm sorry if my answer is not specific enough, but I flatly don't KNOW any universal rule that covers all the stuff we fallible little beings can contrive to burden ourselves with.