re: That you can kill your own baby and get away with murder is well known...

The reason weeks are usually used is because of the changes expected based on certain weeks of gestation and the fact that ___ weeks and ___ days is the common way OBs keep track of gestational age and monitor the pregnancy. And it's been that way since before abortions were legal.

I don't think anyone does it as a way of making the life seem less significant (assuming that's what you meant and I could be incorrect in that assumption).

Stuff like this is terrible regardless of how the age is measured or what age it is for that matter.