First example:
That action would be immoral if we look at the world today, adoption is possible as well.
So if women wants one child, giving birth to another wouldn’t make her situation worse, so she would be justified in killing it.
If there was an example where food had enough food just for her and one child, and had no help, than l think killing the other fetus would be justified.
Second example:
This really depends on the intention, if women REALLY just didn’t want her child to suffer, than l think she would be MORALLY justified(she wouldn’t act immorally), intentions matter.
l see things like death, pain, and lack of freedom as intrinsically bad things, and health,life and freedom as intrinsically good. Those things can’t ever be not bad.
Someone can however have a justification for actions that would result in loss of those things.
That does seem to be an arbitrary naturalistic distinction, why would it matter that one is natural and other one isn’t?