Interesting moral discussion: An estimated 8000 fewer births in 2017 attributed to a law that saved an estimated 57 lives in the same year.
But it is an interesting thing to think about. Sure, 57 children dying would create a lot of misery for a family (and extended family), but would 8,000 other children in the world, presumably giving their families happiness, somehow "make up for it"?
Feels odd to think about it in those terms. Balancing/trading lives is a dirty business.
I imagine the typical car accident in which three 'car seat age' children are involved, and at least one is killed. Then I imagine the typical event where a family decide against a third child. I feel quite a substantial qualitative difference! I certainly wouldn't claim one offsets the other.
Personally I don't know if there's any multiplier I'd accept. I find reduction of suffering and trauma much more important to me than offset creation of life and opportunity.