Book of Mormon Citation- Does 3Nephi 1:13 mean abortion is okay?

The verse in question:

Lift up your head and be of good cheer; for behold, the time is at hand, and on this night shall the sign be given, and on the morrow come I into the world, to show unto the world that I will fulfil all that which I have caused to be spoken by the mouth of my holy prophets.

If Jesus comes into the world the day after this verse, but Mary had been pregnant long before, with the sign being the star signifying Christ’s birth, then doesn’t that mean the spirit doesn’t enter the body until the day of birth, in which case, there’s no justification against abortion other than individual preference?