With religious contraints removed, what now guides our ethics regarding protection of human life. Believers have concepts like sanctity of life, the existence of a soul (whatever that is), all life a gift of God. only God can take away, etc etc. So what guides agnostics in deciding when, if ever, to allow termination of a developing life? Where to draw a line on terminations is obviously a serious issue and it would be interesting to see where Agnostics draw a line. And precisely why.

Human babies start to interact at about three months, at which point they are just starting to behave like humans rather than being just cute feeders. Which seems like a sensible upper limit.

So my question is:

If, before birth there is a medically proven risk of, or after birth there are obvious signs of, severe genetic defects, AND the mother wishes it, up to what point should we legally allow life to be humanely terminated?

(I'm restricting it to genetic defect issues, which incidentally affect about 5% of embryos, I know there are others like rape, economic, social etc but let's keep it focused on defects)